<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:82be3433-c58e-4ce3-8a9d-78b8e8a6f4e7,g:6657a624-7b30-480f-8dff-39c7ed6ae323-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.gentex.com/role/UNAUDITEDCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSINVESTMENT" xlink:type="simple" xlink:href="gntx-20260331.xsd#UNAUDITEDCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSINVESTMENT"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/UNAUDITEDCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSINVESTMENT" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_5d3c1673-0f25-4352-9f48-702e8e00125a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_411c853f-70fd-4c28-b466-8af9f7ab6aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_5d3c1673-0f25-4352-9f48-702e8e00125a" xlink:to="loc_us-gaap_StatementTable_411c853f-70fd-4c28-b466-8af9f7ab6aa8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_0d5553a1-de4b-405e-b18b-cc052f6d9cd1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_411c853f-70fd-4c28-b466-8af9f7ab6aa8" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_0d5553a1-de4b-405e-b18b-cc052f6d9cd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_0d5553a1-de4b-405e-b18b-cc052f6d9cd1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_0d5553a1-de4b-405e-b18b-cc052f6d9cd1" xlink:to="loc_us-gaap_EquityComponentDomain_0d5553a1-de4b-405e-b18b-cc052f6d9cd1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_c049b8be-e1ef-493a-9508-5886ebbcc35f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_0d5553a1-de4b-405e-b18b-cc052f6d9cd1" xlink:to="loc_us-gaap_EquityComponentDomain_c049b8be-e1ef-493a-9508-5886ebbcc35f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_530584fe-daea-4573-81f4-1fb40757e0ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_c049b8be-e1ef-493a-9508-5886ebbcc35f" xlink:to="loc_us-gaap_ParentMember_530584fe-daea-4573-81f4-1fb40757e0ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_dab1178e-a7a3-4a15-bcbd-9b74f147ac8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_530584fe-daea-4573-81f4-1fb40757e0ea" xlink:to="loc_us-gaap_CommonStockMember_dab1178e-a7a3-4a15-bcbd-9b74f147ac8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_ba60a2d1-0630-4e17-94f3-17336f125985" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_530584fe-daea-4573-81f4-1fb40757e0ea" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_ba60a2d1-0630-4e17-94f3-17336f125985" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_028cf981-4998-44ea-a055-39938cd3007d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_530584fe-daea-4573-81f4-1fb40757e0ea" xlink:to="loc_us-gaap_RetainedEarningsMember_028cf981-4998-44ea-a055-39938cd3007d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_6ffcbb26-16f3-4e9e-bc59-2b1e06703d30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_530584fe-daea-4573-81f4-1fb40757e0ea" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_6ffcbb26-16f3-4e9e-bc59-2b1e06703d30" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_76095ca4-b7d4-4eb5-95df-628e72696e3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_c049b8be-e1ef-493a-9508-5886ebbcc35f" xlink:to="loc_us-gaap_NoncontrollingInterestMember_76095ca4-b7d4-4eb5-95df-628e72696e3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_5d3c1673-0f25-4352-9f48-702e8e00125a" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_3a306340-59a1-40cf-906a-71bfff066cdd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_3a306340-59a1-40cf-906a-71bfff066cdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_b7796da2-6edc-466a-9ce0-6cfdb81fe92d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_b7796da2-6edc-466a-9ce0-6cfdb81fe92d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_ccd37627-32dc-4a90-a63a-00a5e4274989" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_ccd37627-32dc-4a90-a63a-00a5e4274989" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_ac082fca-a665-4397-9500-a58643daf09c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_ac082fca-a665-4397-9500-a58643daf09c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_a731c4a8-cd9b-4f15-ab98-3087f9e33169" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_a731c4a8-cd9b-4f15-ab98-3087f9e33169" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_b8fa42ca-ed6d-473b-ac50-c4016778696a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_b8fa42ca-ed6d-473b-ac50-c4016778696a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_c197fc77-52ce-4107-a6cf-51c4a3f0c51b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_c197fc77-52ce-4107-a6cf-51c4a3f0c51b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_a34bd979-a5a4-433c-baef-4379af9725f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_DividendsCommonStockCash_a34bd979-a5a4-433c-baef-4379af9725f1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest_601c1ae3-7454-4cb7-8c77-7aca69fdd887" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest_601c1ae3-7454-4cb7-8c77-7aca69fdd887" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_eae9e94c-9ad5-41be-ac53-bc893fcf3fbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_eae9e94c-9ad5-41be-ac53-bc893fcf3fbd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_941966eb-6992-4aad-bef8-d5ae5d6714aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_ef3384fb-5ef5-4d85-9622-5dcf6b2a5ddb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_941966eb-6992-4aad-bef8-d5ae5d6714aa" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_70fd0512-b240-4add-999d-b0e910c05e13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_cded236a-a510-4e04-831e-7808f3e340ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsScheduleofGoodwillDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#GoodwillandOtherIntangibleAssetsScheduleofGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsScheduleofGoodwillDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_019cd62e-fc50-73b4-9c53-41ee40161de8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_019cd62e-fc50-7723-a847-30e951e8de8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_019cd62e-fc50-73b4-9c53-41ee40161de8" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_019cd62e-fc50-7723-a847-30e951e8de8d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019cd62e-fc50-7e2f-8cdc-304a438fa77b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_019cd62e-fc50-7723-a847-30e951e8de8d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019cd62e-fc50-7e2f-8cdc-304a438fa77b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019cd62e-fc50-7e2f-8cdc-304a438fa77b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019cd62e-fc50-7e2f-8cdc-304a438fa77b" xlink:to="loc_us-gaap_SegmentDomain_019cd62e-fc50-7e2f-8cdc-304a438fa77b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019cd62e-fc50-7110-b716-16c7ce85db92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019cd62e-fc50-7e2f-8cdc-304a438fa77b" xlink:to="loc_us-gaap_SegmentDomain_019cd62e-fc50-7110-b716-16c7ce85db92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AutomotiveProductsSegmentMember_019cd62e-fc50-7597-8d5a-9236bf57eee5" xlink:href="gntx-20260331.xsd#gntx_AutomotiveProductsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019cd62e-fc50-7110-b716-16c7ce85db92" xlink:to="loc_gntx_AutomotiveProductsSegmentMember_019cd62e-fc50-7597-8d5a-9236bf57eee5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PremiumAudioProductsSegmentMember_019cd62e-fc50-7e9e-b1c5-dd584a4e8bc7" xlink:href="gntx-20260331.xsd#gntx_PremiumAudioProductsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019cd62e-fc50-7110-b716-16c7ce85db92" xlink:to="loc_gntx_PremiumAudioProductsSegmentMember_019cd62e-fc50-7e9e-b1c5-dd584a4e8bc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherSegmentsMember_019cd62e-fc50-732e-8ad5-db25d85953f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllOtherSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019cd62e-fc50-7110-b716-16c7ce85db92" xlink:to="loc_us-gaap_AllOtherSegmentsMember_019cd62e-fc50-732e-8ad5-db25d85953f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_9262f2c0-671e-4400-98e6-215145bf8909" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019cd62e-fc50-73b4-9c53-41ee40161de8" xlink:to="loc_us-gaap_GoodwillRollForward_9262f2c0-671e-4400-98e6-215145bf8909" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_385f73ac-e4e5-4912-9720-7547c381776d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_9262f2c0-671e-4400-98e6-215145bf8909" xlink:to="loc_us-gaap_Goodwill_385f73ac-e4e5-4912-9720-7547c381776d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPeriodIncreaseDecrease_019d65c0-c6fd-7d61-9301-0d2aed8b28cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_9262f2c0-671e-4400-98e6-215145bf8909" xlink:to="loc_us-gaap_GoodwillPeriodIncreaseDecrease_019d65c0-c6fd-7d61-9301-0d2aed8b28cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_019d9072-afb3-757f-865f-aede0d7fe1d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_9262f2c0-671e-4400-98e6-215145bf8909" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_019d9072-afb3-757f-865f-aede0d7fe1d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_019d9078-0b6b-7357-a883-03393e166bab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_9262f2c0-671e-4400-98e6-215145bf8909" xlink:to="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_019d9078-0b6b-7357-a883-03393e166bab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_88f230ee-ae67-4721-adc3-c49be17719d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillGross_9b18b162-9d9b-4680-b55c-6be3e7a59e95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019cd62e-fc50-73b4-9c53-41ee40161de8" xlink:to="loc_us-gaap_GoodwillGross_9b18b162-9d9b-4680-b55c-6be3e7a59e95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_8c06bbe1-e515-4c52-bf33-7c9a85dce826" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019cd62e-fc50-73b4-9c53-41ee40161de8" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_8c06bbe1-e515-4c52-bf33-7c9a85dce826" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_66b2bc47-341b-490a-ac66-c20427bd7b33" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsNarrativeDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#GoodwillandOtherIntangibleAssetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dae6b-141c-7ff5-b97e-6e7b9ae9ae55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dae6b-141c-7ff5-b97e-6e7b9ae9ae55" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dae6b-141c-7f12-8284-27007018e271" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dae6b-141c-7ff5-b97e-6e7b9ae9ae55" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dae6b-141c-7f12-8284-27007018e271" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dae6b-141c-7f12-8284-27007018e271_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dae6b-141c-7f12-8284-27007018e271" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dae6b-141c-7f12-8284-27007018e271_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dae6b-141c-748e-a90f-fcd84425842f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019dae6b-141c-7f12-8284-27007018e271" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dae6b-141c-748e-a90f-fcd84425842f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PatentsAndOtherIntangibleAssetsMember_019dae6b-141c-7b8d-84b3-4a01ea2c6d8d" xlink:href="gntx-20260331.xsd#gntx_PatentsAndOtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019dae6b-141c-748e-a90f-fcd84425842f" xlink:to="loc_gntx_PatentsAndOtherIntangibleAssetsMember_019dae6b-141c-7b8d-84b3-4a01ea2c6d8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_019dae6b-edeb-7aaa-a0a7-f2f233af67ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_019dae6b-edeb-7aaa-a0a7-f2f233af67ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019dae6c-15cc-7dba-80fc-7c3abe33223c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019dae6c-15cc-7dba-80fc-7c3abe33223c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019dae6c-15cc-7541-b00b-24a0d8f052d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019dae6c-15cc-7541-b00b-24a0d8f052d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019dae6c-15cc-7a87-99ff-c82bd4422ced" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019dae6c-15cc-7a87-99ff-c82bd4422ced" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019dae6c-15cc-7ec6-b68e-8f06f7a93613" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019dae6c-15cc-7ec6-b68e-8f06f7a93613" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019dae6c-15cc-7d0f-b5ea-d7dbab9b1f3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019dae6c-15cc-7d0f-b5ea-d7dbab9b1f3e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019dae6c-15cc-7cff-ad12-c12cf3d05497" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dae6b-141c-7298-8782-f2fe26f2b714" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019dae6c-15cc-7cff-ad12-c12cf3d05497" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#GoodwillandOtherIntangibleAssetsScheduleofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dbba141e-74bc-49b2-9906-9076ce8f4dfb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dbba141e-74bc-49b2-9906-9076ce8f4dfb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_6487e8c9-fc2b-4636-9a5e-c72b014a315f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dbba141e-74bc-49b2-9906-9076ce8f4dfb" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_6487e8c9-fc2b-4636-9a5e-c72b014a315f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_6487e8c9-fc2b-4636-9a5e-c72b014a315f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_6487e8c9-fc2b-4636-9a5e-c72b014a315f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_6487e8c9-fc2b-4636-9a5e-c72b014a315f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_6487e8c9-fc2b-4636-9a5e-c72b014a315f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_HomeLinkMember_e7bbcc6c-b446-4b74-8774-5099f16a1ed8" xlink:href="gntx-20260331.xsd#gntx_HomeLinkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:to="loc_gntx_HomeLinkMember_e7bbcc6c-b446-4b74-8774-5099f16a1ed8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BioCenturionLLCMember_e03a48a4-3392-4b21-9bb0-cff195bd9334" xlink:href="gntx-20260331.xsd#gntx_BioCenturionLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:to="loc_gntx_BioCenturionLLCMember_e03a48a4-3392-4b21-9bb0-cff195bd9334" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ESightCorporationMember_b49a2cbb-28c2-4e92-a44c-e3b9e4a62587" xlink:href="gntx-20260331.xsd#gntx_ESightCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:to="loc_gntx_ESightCorporationMember_b49a2cbb-28c2-4e92-a44c-e3b9e4a62587" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BioConnectInc.Member_69434c37-2126-4c5b-8a55-84e507279fe6" xlink:href="gntx-20260331.xsd#gntx_BioConnectInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:to="loc_gntx_BioConnectInc.Member_69434c37-2126-4c5b-8a55-84e507279fe6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_VaporsensInc.Member_2e70fcb9-6fd0-4be5-a8bd-3f87e5e202a2" xlink:href="gntx-20260331.xsd#gntx_VaporsensInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:to="loc_gntx_VaporsensInc.Member_2e70fcb9-6fd0-4be5-a8bd-3f87e5e202a2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ArgilIncMember_fb3687ca-bac9-4d2f-95c2-bfbf96b99393" xlink:href="gntx-20260331.xsd#gntx_ArgilIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:to="loc_gntx_ArgilIncMember_fb3687ca-bac9-4d2f-95c2-bfbf96b99393" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AirCraftGlassProductionBVMember_c3264196-8e5e-4f12-a60d-cbb0fdade114" xlink:href="gntx-20260331.xsd#gntx_AirCraftGlassProductionBVMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:to="loc_gntx_AirCraftGlassProductionBVMember_c3264196-8e5e-4f12-a60d-cbb0fdade114" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_GuardianOpticalTechnologiesMember_46b88181-8582-4ee7-9ea7-726f9f372324" xlink:href="gntx-20260331.xsd#gntx_GuardianOpticalTechnologiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b3592b10-35f7-4610-8169-54f3e4f4ca69" xlink:to="loc_gntx_GuardianOpticalTechnologiesMember_46b88181-8582-4ee7-9ea7-726f9f372324" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_70c5b6ca-47cb-429e-944f-09735f5f9ad8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dbba141e-74bc-49b2-9906-9076ce8f4dfb" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_70c5b6ca-47cb-429e-944f-09735f5f9ad8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_70c5b6ca-47cb-429e-944f-09735f5f9ad8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_70c5b6ca-47cb-429e-944f-09735f5f9ad8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_70c5b6ca-47cb-429e-944f-09735f5f9ad8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_970246b0-3a8f-4049-968f-40c34efa5c58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_70c5b6ca-47cb-429e-944f-09735f5f9ad8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_970246b0-3a8f-4049-968f-40c34efa5c58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PatentsAndOtherIntangibleAssetsMember_019ce350-2c1d-7594-87b9-3bb900591c1d" xlink:href="gntx-20260331.xsd#gntx_PatentsAndOtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_970246b0-3a8f-4049-968f-40c34efa5c58" xlink:to="loc_gntx_PatentsAndOtherIntangibleAssetsMember_019ce350-2c1d-7594-87b9-3bb900591c1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentsMember_7162903b-4feb-450a-8180-fa041ac6bc72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_PatentsAndOtherIntangibleAssetsMember_019ce350-2c1d-7594-87b9-3bb900591c1d" xlink:to="loc_us-gaap_PatentsMember_7162903b-4feb-450a-8180-fa041ac6bc72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_00c0fd5c-4475-4b7a-a51c-8b38dc3642fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_PatentsAndOtherIntangibleAssetsMember_019ce350-2c1d-7594-87b9-3bb900591c1d" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_00c0fd5c-4475-4b7a-a51c-8b38dc3642fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_973ebd31-f907-40da-8257-4d7a4f5ef4a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_00c0fd5c-4475-4b7a-a51c-8b38dc3642fe" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_973ebd31-f907-40da-8257-4d7a4f5ef4a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerContractsMember_32dce516-696e-4ddd-a8dd-8b6c9a9fad61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_00c0fd5c-4475-4b7a-a51c-8b38dc3642fe" xlink:to="loc_us-gaap_CustomerContractsMember_32dce516-696e-4ddd-a8dd-8b6c9a9fad61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_ebb46bcf-6557-4ab9-b537-2ec431026b3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_00c0fd5c-4475-4b7a-a51c-8b38dc3642fe" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_ebb46bcf-6557-4ab9-b537-2ec431026b3f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_32346e92-24cf-4215-9887-d76cb09c2020" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_00c0fd5c-4475-4b7a-a51c-8b38dc3642fe" xlink:to="loc_us-gaap_CustomerRelationshipsMember_32346e92-24cf-4215-9887-d76cb09c2020" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_f600e123-2b4c-4478-80cd-6bc245df1e0d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dbba141e-74bc-49b2-9906-9076ce8f4dfb" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_f600e123-2b4c-4478-80cd-6bc245df1e0d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_f600e123-2b4c-4478-80cd-6bc245df1e0d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_f600e123-2b4c-4478-80cd-6bc245df1e0d" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_f600e123-2b4c-4478-80cd-6bc245df1e0d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_50879aeb-da2c-43ff-84e4-45715557b006" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_f600e123-2b4c-4478-80cd-6bc245df1e0d" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_50879aeb-da2c-43ff-84e4-45715557b006" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_f2fabbe1-bf7f-42dc-902c-386fa5c23699" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_50879aeb-da2c-43ff-84e4-45715557b006" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_f2fabbe1-bf7f-42dc-902c-386fa5c23699" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicensingAgreementsMember_42f2694e-935e-4629-a89e-8658b0148ebd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LicensingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_50879aeb-da2c-43ff-84e4-45715557b006" xlink:to="loc_us-gaap_LicensingAgreementsMember_42f2694e-935e-4629-a89e-8658b0148ebd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_1bc75c12-9b92-4d1d-ba13-287ce0a71ddd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_50879aeb-da2c-43ff-84e4-45715557b006" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_1bc75c12-9b92-4d1d-ba13-287ce0a71ddd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_35965191-4dee-44a8-be2b-a3584d242205" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_35965191-4dee-44a8-be2b-a3584d242205" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_0b96416d-6c4d-4d51-be52-cdf1c14ff2ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_0b96416d-6c4d-4d51-be52-cdf1c14ff2ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_db55bab2-3f2b-4b96-b4bc-007adfc39812" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_db55bab2-3f2b-4b96-b4bc-007adfc39812" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d644e48e-6cf6-4559-819b-9984b243622d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d644e48e-6cf6-4559-819b-9984b243622d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_24bd1dff-4bc5-4a30-bf76-bcd7ab94c510" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_24bd1dff-4bc5-4a30-bf76-bcd7ab94c510" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_244534a2-5776-47e7-890a-9a65bb55ebea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_244534a2-5776-47e7-890a-9a65bb55ebea" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_IntangiblePatentsAndAssetsGrossExcludingGoodwill_019ce350-9712-7a7a-87af-4a3ce524c90c" xlink:href="gntx-20260331.xsd#gntx_IntangiblePatentsAndAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_gntx_IntangiblePatentsAndAssetsGrossExcludingGoodwill_019ce350-9712-7a7a-87af-4a3ce524c90c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_FiniteLivedIntangiblePatentsAndAssetsAccumulatedAmortization_019ce350-9712-73c9-869d-28af9b9b814f" xlink:href="gntx-20260331.xsd#gntx_FiniteLivedIntangiblePatentsAndAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_gntx_FiniteLivedIntangiblePatentsAndAssetsAccumulatedAmortization_019ce350-9712-73c9-869d-28af9b9b814f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_IntangiblePatentsAndAssetsNetExcludingGoodwill_019ce350-9712-763b-88d0-8cac316d0d8a" xlink:href="gntx-20260331.xsd#gntx_IntangiblePatentsAndAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_gntx_IntangiblePatentsAndAssetsNetExcludingGoodwill_019ce350-9712-763b-88d0-8cac316d0d8a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_2b18257c-2850-4e19-beb2-41efa313d3b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_24c4720e-3bcf-4808-afe0-9df0c32d5c00" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_2b18257c-2850-4e19-beb2-41efa313d3b3" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/InvestmentsNarrativeDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#InvestmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/InvestmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_5504c79a-d0e9-4536-bb07-10d32caee312" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_5504c79a-d0e9-4536-bb07-10d32caee312" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019d6e2f-bd30-7c7d-8a9a-3a3922f52e6b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_5504c79a-d0e9-4536-bb07-10d32caee312" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019d6e2f-bd30-7c7d-8a9a-3a3922f52e6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019d6e2f-bd30-7c7d-8a9a-3a3922f52e6b_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019d6e2f-bd30-7c7d-8a9a-3a3922f52e6b" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019d6e2f-bd30-7c7d-8a9a-3a3922f52e6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019d6e2f-bd30-77c0-9dd1-2185aa99c373" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019d6e2f-bd30-7c7d-8a9a-3a3922f52e6b" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019d6e2f-bd30-77c0-9dd1-2185aa99c373" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AsaElectronicsLLCAndSubsidiaryMember_019d6e2f-bd30-73c8-9004-7ad68d241678" xlink:href="gntx-20260331.xsd#gntx_AsaElectronicsLLCAndSubsidiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019d6e2f-bd30-77c0-9dd1-2185aa99c373" xlink:to="loc_gntx_AsaElectronicsLLCAndSubsidiaryMember_019d6e2f-bd30-73c8-9004-7ad68d241678" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AdaskyInvestmentMember_019d6e2f-bd30-75a7-91e2-4b418a7a6d18" xlink:href="gntx-20260331.xsd#gntx_AdaskyInvestmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019d6e2f-bd30-77c0-9dd1-2185aa99c373" xlink:to="loc_gntx_AdaskyInvestmentMember_019d6e2f-bd30-75a7-91e2-4b418a7a6d18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019d6e2f-bd30-7537-ba64-10743d24bbd2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019d6e2f-bd30-7537-ba64-10743d24bbd2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_019d6e2f-bd30-7791-97d4-b0dc4f096f38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_EquityMethodInvestments_019d6e2f-bd30-7791-97d4-b0dc4f096f38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_019d6e2f-bd30-726a-a8b7-f894e47cb8e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_019d6e2f-bd30-726a-a8b7-f894e47cb8e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFVNINoncurrent_019d6e2f-bd30-7215-9baa-bcd360de57e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFVNINoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_EquitySecuritiesFVNINoncurrent_019d6e2f-bd30-7215-9baa-bcd360de57e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019d6e2f-bd30-76f8-84c4-92fdb3872f79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019d6e2f-bd30-76f8-84c4-92fdb3872f79" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiRealizedGainLoss_019d6e2f-bd30-7ab6-84cb-88ce786d9999" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_EquitySecuritiesFvNiRealizedGainLoss_019d6e2f-bd30-7ab6-84cb-88ce786d9999" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment_019d6e2f-bd30-75f5-884e-01200c149320" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment_019d6e2f-bd30-75f5-884e-01200c149320" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_EquityMethodInvestmentForbearanceAgreementAmount_019dae58-8356-7022-bcda-9c47f12a8989" xlink:href="gntx-20260331.xsd#gntx_EquityMethodInvestmentForbearanceAgreementAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_gntx_EquityMethodInvestmentForbearanceAgreementAmount_019dae58-8356-7022-bcda-9c47f12a8989" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease_019d6e2f-f7db-76a9-aa54-d198267211a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease_019d6e2f-f7db-76a9-aa54-d198267211a3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForNotesAndLoansReceivableCurrent_019daba3-bc74-718c-b861-a49e7e764ed3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllowanceForNotesAndLoansReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_AllowanceForNotesAndLoansReceivableCurrent_019daba3-bc74-718c-b861-a49e7e764ed3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesAndLoansReceivableNetCurrent_019d6e2f-f7db-7804-956c-d8e8261acdc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesAndLoansReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_NotesAndLoansReceivableNetCurrent_019d6e2f-f7db-7804-956c-d8e8261acdc9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesAndLoansReceivableNetNoncurrent_019d6e2f-f7db-7ad8-a061-b83176d52da1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesAndLoansReceivableNetNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_1837d0d9-c5bc-4e5e-9148-8784ad5f1306" xlink:to="loc_us-gaap_NotesAndLoansReceivableNetNoncurrent_019d6e2f-f7db-7ad8-a061-b83176d52da1" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/InvestmentsScheduleofAssetsorLiabilitiesHavingRecurringMeasurementsDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#InvestmentsScheduleofAssetsorLiabilitiesHavingRecurringMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/InvestmentsScheduleofAssetsorLiabilitiesHavingRecurringMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_25f5e003-729f-43a6-b547-6f07f37e713d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b08a3fef-c603-496e-80c8-69854150b9fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_25f5e003-729f-43a6-b547-6f07f37e713d" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b08a3fef-c603-496e-80c8-69854150b9fb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_e8169ae1-c6b5-4b42-b2f6-fc28344ac8c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b08a3fef-c603-496e-80c8-69854150b9fb" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_e8169ae1-c6b5-4b42-b2f6-fc28344ac8c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_e8169ae1-c6b5-4b42-b2f6-fc28344ac8c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_e8169ae1-c6b5-4b42-b2f6-fc28344ac8c9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_e8169ae1-c6b5-4b42-b2f6-fc28344ac8c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_93390d21-1cdc-43c3-b8d3-01d162eb082e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_e8169ae1-c6b5-4b42-b2f6-fc28344ac8c9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_93390d21-1cdc-43c3-b8d3-01d162eb082e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_286607e2-0825-4554-b16e-ee7ff7346ee1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_93390d21-1cdc-43c3-b8d3-01d162eb082e" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_286607e2-0825-4554-b16e-ee7ff7346ee1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_b4469f29-c35f-42ef-a6ad-7f956c8d169e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_93390d21-1cdc-43c3-b8d3-01d162eb082e" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_b4469f29-c35f-42ef-a6ad-7f956c8d169e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_06bfceb1-c8d3-481d-b8fa-b40adceb3a72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_93390d21-1cdc-43c3-b8d3-01d162eb082e" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_06bfceb1-c8d3-481d-b8fa-b40adceb3a72" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_031e131f-2714-4f19-bdcc-e1b89484a606" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b08a3fef-c603-496e-80c8-69854150b9fb" xlink:to="loc_us-gaap_InvestmentTypeAxis_031e131f-2714-4f19-bdcc-e1b89484a606" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_031e131f-2714-4f19-bdcc-e1b89484a606_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_031e131f-2714-4f19-bdcc-e1b89484a606" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_031e131f-2714-4f19-bdcc-e1b89484a606_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_95d91818-38b9-47d5-b65c-b05db0768dbe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_031e131f-2714-4f19-bdcc-e1b89484a606" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_95d91818-38b9-47d5-b65c-b05db0768dbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_d8ebd221-b1fc-4bd0-bc1f-b2ade0b58962" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_95d91818-38b9-47d5-b65c-b05db0768dbe" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_d8ebd221-b1fc-4bd0-bc1f-b2ade0b58962" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_07c1582a-3aaa-47f7-b17f-4a3887128f73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLongTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_95d91818-38b9-47d5-b65c-b05db0768dbe" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_07c1582a-3aaa-47f7-b17f-4a3887128f73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_0d4104dd-dbb8-4689-a36d-19a1ed981348" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b08a3fef-c603-496e-80c8-69854150b9fb" xlink:to="loc_us-gaap_FinancialInstrumentAxis_0d4104dd-dbb8-4689-a36d-19a1ed981348" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0d4104dd-dbb8-4689-a36d-19a1ed981348_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_0d4104dd-dbb8-4689-a36d-19a1ed981348" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0d4104dd-dbb8-4689-a36d-19a1ed981348_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_ba1526b2-243b-4e8b-ac5e-1263b20db3c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_0d4104dd-dbb8-4689-a36d-19a1ed981348" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_ba1526b2-243b-4e8b-ac5e-1263b20db3c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_27298d48-bf76-4c89-86f9-09298281b95b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_ba1526b2-243b-4e8b-ac5e-1263b20db3c3" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_27298d48-bf76-4c89-86f9-09298281b95b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_526d2d0c-5021-4037-a881-dfbeec67d2b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_ba1526b2-243b-4e8b-ac5e-1263b20db3c3" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_526d2d0c-5021-4037-a881-dfbeec67d2b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MunicipalBondsMember_5d9aafc6-c5c3-4a64-ad24-37be3bdf3b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MunicipalBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_ba1526b2-243b-4e8b-ac5e-1263b20db3c3" xlink:to="loc_us-gaap_MunicipalBondsMember_5d9aafc6-c5c3-4a64-ad24-37be3bdf3b1f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDebtSecuritiesMember_75391ebd-7925-45dd-8fda-86c7548554d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_ba1526b2-243b-4e8b-ac5e-1263b20db3c3" xlink:to="loc_us-gaap_OtherDebtSecuritiesMember_75391ebd-7925-45dd-8fda-86c7548554d2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_c055f543-6015-47ca-95b8-ee9ad23f146c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_25f5e003-729f-43a6-b547-6f07f37e713d" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_c055f543-6015-47ca-95b8-ee9ad23f146c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_f1a8949d-4407-4830-bf44-f18dd487d96a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_25f5e003-729f-43a6-b547-6f07f37e713d" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_f1a8949d-4407-4830-bf44-f18dd487d96a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_39a48c34-b7a8-453f-903e-c037be7cab79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_25f5e003-729f-43a6-b547-6f07f37e713d" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_39a48c34-b7a8-453f-903e-c037be7cab79" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/InvestmentsScheduleofAmortizedCostUnrealizedGainsandLossesandMarketValueofInvestmentSecuritiesDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#InvestmentsScheduleofAmortizedCostUnrealizedGainsandLossesandMarketValueofInvestmentSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/InvestmentsScheduleofAmortizedCostUnrealizedGainsandLossesandMarketValueofInvestmentSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_2aafc5a8-63e5-4ce5-950e-3693c3e9d7a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_4d67ce3c-da64-4b40-83e5-91e73a791a2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_2aafc5a8-63e5-4ce5-950e-3693c3e9d7a2" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_4d67ce3c-da64-4b40-83e5-91e73a791a2a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_InvestmentLengthAxis_019ce32d-1bcf-71bf-8ce4-5ad3ee4db1e5" xlink:href="gntx-20260331.xsd#gntx_InvestmentLengthAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_4d67ce3c-da64-4b40-83e5-91e73a791a2a" xlink:to="loc_gntx_InvestmentLengthAxis_019ce32d-1bcf-71bf-8ce4-5ad3ee4db1e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_InvestmentLengthDomain_019ce32d-1bcf-71bf-8ce4-5ad3ee4db1e5_default" xlink:href="gntx-20260331.xsd#gntx_InvestmentLengthDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gntx_InvestmentLengthAxis_019ce32d-1bcf-71bf-8ce4-5ad3ee4db1e5" xlink:to="loc_gntx_InvestmentLengthDomain_019ce32d-1bcf-71bf-8ce4-5ad3ee4db1e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_InvestmentLengthDomain_019ce32d-1bcf-7c57-b8a2-7d0026211fb1" xlink:href="gntx-20260331.xsd#gntx_InvestmentLengthDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gntx_InvestmentLengthAxis_019ce32d-1bcf-71bf-8ce4-5ad3ee4db1e5" xlink:to="loc_gntx_InvestmentLengthDomain_019ce32d-1bcf-7c57-b8a2-7d0026211fb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_019ce319-bc9f-76cd-8285-8fce8c8e0263" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_InvestmentLengthDomain_019ce32d-1bcf-7c57-b8a2-7d0026211fb1" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_019ce319-bc9f-76cd-8285-8fce8c8e0263" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_019ce319-bc9f-7738-b7f3-bd3180d4024f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLongTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_InvestmentLengthDomain_019ce32d-1bcf-7c57-b8a2-7d0026211fb1" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_019ce319-bc9f-7738-b7f3-bd3180d4024f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_542b9862-4a6d-40f5-813a-8229edeaf82e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_4d67ce3c-da64-4b40-83e5-91e73a791a2a" xlink:to="loc_us-gaap_FinancialInstrumentAxis_542b9862-4a6d-40f5-813a-8229edeaf82e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_542b9862-4a6d-40f5-813a-8229edeaf82e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_542b9862-4a6d-40f5-813a-8229edeaf82e" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_542b9862-4a6d-40f5-813a-8229edeaf82e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f71f78ab-c308-413a-94ce-819b2fca30e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_542b9862-4a6d-40f5-813a-8229edeaf82e" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f71f78ab-c308-413a-94ce-819b2fca30e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_0f266a00-e1c3-4f6a-9d8b-168b7132c756" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f71f78ab-c308-413a-94ce-819b2fca30e7" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_0f266a00-e1c3-4f6a-9d8b-168b7132c756" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MunicipalBondsMember_2127662a-cc1c-41fa-8cea-2abd85ed4610" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MunicipalBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f71f78ab-c308-413a-94ce-819b2fca30e7" xlink:to="loc_us-gaap_MunicipalBondsMember_2127662a-cc1c-41fa-8cea-2abd85ed4610" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDebtSecuritiesMember_31e8742a-a6db-4032-ac50-46318389d7f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f71f78ab-c308-413a-94ce-819b2fca30e7" xlink:to="loc_us-gaap_OtherDebtSecuritiesMember_31e8742a-a6db-4032-ac50-46318389d7f8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_328dbaf9-3ddf-4221-b32f-93fc8b9d3b7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f71f78ab-c308-413a-94ce-819b2fca30e7" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_328dbaf9-3ddf-4221-b32f-93fc8b9d3b7d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_72bb61bc-a78b-46c5-951e-38f93945d2a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_2aafc5a8-63e5-4ce5-950e-3693c3e9d7a2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_72bb61bc-a78b-46c5-951e-38f93945d2a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_7c847b9b-bcf4-4c0a-898e-dd40a3f44cab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_2aafc5a8-63e5-4ce5-950e-3693c3e9d7a2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_7c847b9b-bcf4-4c0a-898e-dd40a3f44cab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_7460c9db-9919-44e9-9cc0-a7b4a64c3819" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_2aafc5a8-63e5-4ce5-950e-3693c3e9d7a2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_7460c9db-9919-44e9-9cc0-a7b4a64c3819" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019cdbc3-6795-7641-927c-567e7505f4a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_2aafc5a8-63e5-4ce5-950e-3693c3e9d7a2" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019cdbc3-6795-7641-927c-567e7505f4a8" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/InvestmentsScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#InvestmentsScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/InvestmentsScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0d8c03d6-497f-4906-8063-7d2f0a513471" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_1008d56b-9b48-4bed-b582-706394ff542f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0d8c03d6-497f-4906-8063-7d2f0a513471" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_1008d56b-9b48-4bed-b582-706394ff542f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_397a854c-3dce-4b30-8cda-3d442f5297c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_1008d56b-9b48-4bed-b582-706394ff542f" xlink:to="loc_us-gaap_FinancialInstrumentAxis_397a854c-3dce-4b30-8cda-3d442f5297c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_397a854c-3dce-4b30-8cda-3d442f5297c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_397a854c-3dce-4b30-8cda-3d442f5297c2" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_397a854c-3dce-4b30-8cda-3d442f5297c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1c8f634d-febb-4a3a-9a3e-796b9edb6bb0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_397a854c-3dce-4b30-8cda-3d442f5297c2" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1c8f634d-febb-4a3a-9a3e-796b9edb6bb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_01a5efc0-8d7a-4584-a2ae-c103f487e25c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FixedIncomeSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1c8f634d-febb-4a3a-9a3e-796b9edb6bb0" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_01a5efc0-8d7a-4584-a2ae-c103f487e25c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_37d2585b-a99b-46ee-a370-053a873ec55d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0d8c03d6-497f-4906-8063-7d2f0a513471" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_37d2585b-a99b-46ee-a370-053a873ec55d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_d2a7acbd-55c2-4b02-812c-be10c0fa9055" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0d8c03d6-497f-4906-8063-7d2f0a513471" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_d2a7acbd-55c2-4b02-812c-be10c0fa9055" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_DebtSecuritiesAvailableForSaleFairValueMaturityAllocatedAndSingleMaturityDateAfterFiveYears_60cc0494-a731-4963-ab22-31ed3d041923" xlink:href="gntx-20260331.xsd#gntx_DebtSecuritiesAvailableForSaleFairValueMaturityAllocatedAndSingleMaturityDateAfterFiveYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0d8c03d6-497f-4906-8063-7d2f0a513471" xlink:to="loc_gntx_DebtSecuritiesAvailableForSaleFairValueMaturityAllocatedAndSingleMaturityDateAfterFiveYears_60cc0494-a731-4963-ab22-31ed3d041923" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_781852b5-967e-4cc4-99c0-8ef73c9a974e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0d8c03d6-497f-4906-8063-7d2f0a513471" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_781852b5-967e-4cc4-99c0-8ef73c9a974e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/StockBasedCompensationPlansNarrativeDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#StockBasedCompensationPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/StockBasedCompensationPlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f42c52b6-5260-472f-a16b-586abf507a94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f42c52b6-5260-472f-a16b-586abf507a94" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_788b4899-0c7d-4025-8472-d289496f8c5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f42c52b6-5260-472f-a16b-586abf507a94" xlink:to="loc_us-gaap_AwardTypeAxis_788b4899-0c7d-4025-8472-d289496f8c5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_788b4899-0c7d-4025-8472-d289496f8c5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_788b4899-0c7d-4025-8472-d289496f8c5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_788b4899-0c7d-4025-8472-d289496f8c5d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_99579a56-fb2a-4b11-8133-fc0c8e1ed0cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_788b4899-0c7d-4025-8472-d289496f8c5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_99579a56-fb2a-4b11-8133-fc0c8e1ed0cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockCompensationPlanMember_70c0aca3-5940-4e30-88ec-9b8ce9d95742" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_99579a56-fb2a-4b11-8133-fc0c8e1ed0cd" xlink:to="loc_us-gaap_StockCompensationPlanMember_70c0aca3-5940-4e30-88ec-9b8ce9d95742" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_c0ebacbb-74b1-41de-a149-fc33117fd0aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_99579a56-fb2a-4b11-8133-fc0c8e1ed0cd" xlink:to="loc_us-gaap_PerformanceSharesMember_c0ebacbb-74b1-41de-a149-fc33117fd0aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PerformanceShareAwardsMember_b582c6a4-c30c-477a-8404-09f79fb16bd4" xlink:href="gntx-20260331.xsd#gntx_PerformanceShareAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_99579a56-fb2a-4b11-8133-fc0c8e1ed0cd" xlink:to="loc_gntx_PerformanceShareAwardsMember_b582c6a4-c30c-477a-8404-09f79fb16bd4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_6d5f9447-0f29-4ed9-b6d8-eed8b6fa5eab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f42c52b6-5260-472f-a16b-586abf507a94" xlink:to="loc_us-gaap_PlanNameAxis_6d5f9447-0f29-4ed9-b6d8-eed8b6fa5eab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_6d5f9447-0f29-4ed9-b6d8-eed8b6fa5eab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_6d5f9447-0f29-4ed9-b6d8-eed8b6fa5eab" xlink:to="loc_us-gaap_PlanNameDomain_6d5f9447-0f29-4ed9-b6d8-eed8b6fa5eab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_7d14f44a-9a34-4525-8812-1bcf3de4cc97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_6d5f9447-0f29-4ed9-b6d8-eed8b6fa5eab" xlink:to="loc_us-gaap_PlanNameDomain_7d14f44a-9a34-4525-8812-1bcf3de4cc97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_A2019OmnibusIncentivePlanMember_460bb948-913f-4646-8c37-419dcfe2f5a7" xlink:href="gntx-20260331.xsd#gntx_A2019OmnibusIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_7d14f44a-9a34-4525-8812-1bcf3de4cc97" xlink:to="loc_gntx_A2019OmnibusIncentivePlanMember_460bb948-913f-4646-8c37-419dcfe2f5a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_EmployeeStockOptionPlanMember_f0219286-b9ef-44d5-af32-bf1f7512aa75" xlink:href="gntx-20260331.xsd#gntx_EmployeeStockOptionPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_7d14f44a-9a34-4525-8812-1bcf3de4cc97" xlink:to="loc_gntx_EmployeeStockOptionPlanMember_f0219286-b9ef-44d5-af32-bf1f7512aa75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_SecondRestrictedStockPlanMember_0d83bf86-e462-4e07-a687-cd27dfad73f5" xlink:href="gntx-20260331.xsd#gntx_SecondRestrictedStockPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_7d14f44a-9a34-4525-8812-1bcf3de4cc97" xlink:to="loc_gntx_SecondRestrictedStockPlanMember_0d83bf86-e462-4e07-a687-cd27dfad73f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_A2022GentexCorporationEmployeeStockPurchasePlanMember_5871bdf1-1a76-41da-a3d5-221ebd1e6979" xlink:href="gntx-20260331.xsd#gntx_A2022GentexCorporationEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_7d14f44a-9a34-4525-8812-1bcf3de4cc97" xlink:to="loc_gntx_A2022GentexCorporationEmployeeStockPurchasePlanMember_5871bdf1-1a76-41da-a3d5-221ebd1e6979" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_eb7acc74-ed50-4783-8d09-17ab7a24986f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f42c52b6-5260-472f-a16b-586abf507a94" xlink:to="loc_srt_RangeAxis_eb7acc74-ed50-4783-8d09-17ab7a24986f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_eb7acc74-ed50-4783-8d09-17ab7a24986f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_eb7acc74-ed50-4783-8d09-17ab7a24986f" xlink:to="loc_srt_RangeMember_eb7acc74-ed50-4783-8d09-17ab7a24986f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c35d5776-35d7-497a-adbd-c9fc5d71b83d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_eb7acc74-ed50-4783-8d09-17ab7a24986f" xlink:to="loc_srt_RangeMember_c35d5776-35d7-497a-adbd-c9fc5d71b83d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_cd180a74-e4b0-4275-a363-5630547f0331" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c35d5776-35d7-497a-adbd-c9fc5d71b83d" xlink:to="loc_srt_MinimumMember_cd180a74-e4b0-4275-a363-5630547f0331" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_af9930b3-2739-46b4-8dc7-43fc2b1da1f5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c35d5776-35d7-497a-adbd-c9fc5d71b83d" xlink:to="loc_srt_MaximumMember_af9930b3-2739-46b4-8dc7-43fc2b1da1f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_1be176d1-00a7-4409-b727-f8aa1e9d257e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f42c52b6-5260-472f-a16b-586abf507a94" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_1be176d1-00a7-4409-b727-f8aa1e9d257e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_1be176d1-00a7-4409-b727-f8aa1e9d257e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_1be176d1-00a7-4409-b727-f8aa1e9d257e" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_1be176d1-00a7-4409-b727-f8aa1e9d257e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7271067c-4f93-418e-b077-0eb9fa77468d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_1be176d1-00a7-4409-b727-f8aa1e9d257e" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7271067c-4f93-418e-b077-0eb9fa77468d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_a56213c3-2f45-4c88-b5d6-f34f1309e17c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7271067c-4f93-418e-b077-0eb9fa77468d" xlink:to="loc_us-gaap_EmployeeStockMember_a56213c3-2f45-4c88-b5d6-f34f1309e17c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPlans_9a5aae58-452a-4697-bd1e-cedb87b758e4" xlink:href="gntx-20260331.xsd#gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPlans_9a5aae58-452a-4697-bd1e-cedb87b758e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_aa20ff66-eccb-4505-96b2-4b1e04090221" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_aa20ff66-eccb-4505-96b2-4b1e04090221" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod_019d0f63-1f04-7c25-8d8d-e33ab6d78242" xlink:href="gntx-20260331.xsd#gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod_019d0f63-1f04-7c25-8d8d-e33ab6d78242" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_7717b124-9ba0-4d1f-b645-b90562eede38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_7717b124-9ba0-4d1f-b645-b90562eede38" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_c1405e9c-3771-4190-9567-eae22605cd4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_c1405e9c-3771-4190-9567-eae22605cd4b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_b5fa5cf2-0a46-4df3-83be-44a1fae4df12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_b5fa5cf2-0a46-4df3-83be-44a1fae4df12" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_9e2ded22-c59d-4059-a1ce-31091559db65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_9e2ded22-c59d-4059-a1ce-31091559db65" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_c4db1f1a-c292-4618-bb0c-1997988d4728" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_c4db1f1a-c292-4618-bb0c-1997988d4728" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationRestrictedPeriod_019cd698-4888-7069-9314-3b82884b2210" xlink:href="gntx-20260331.xsd#gntx_ShareBasedCompensationRestrictedPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_gntx_ShareBasedCompensationRestrictedPeriod_019cd698-4888-7069-9314-3b82884b2210" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockExpense_1cdd5e5a-adfc-4840-81a2-a57789478ebf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_RestrictedStockExpense_1cdd5e5a-adfc-4840-81a2-a57789478ebf" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate_00fb4774-2f1e-4f6c-8849-8d46bb224e2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate_00fb4774-2f1e-4f6c-8849-8d46bb224e2b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountRecognizedAsCompensationExpense_9e955c60-d3b3-40e5-97f2-3fcefaf6feda" xlink:href="gntx-20260331.xsd#gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountRecognizedAsCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6afb8481-44f9-45e4-91ed-3e771d66a928" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountRecognizedAsCompensationExpense_9e955c60-d3b3-40e5-97f2-3fcefaf6feda" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/StockBasedCompensationPlansScheduleofSharesIssuedNetofSharesCanceledExpiredDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#StockBasedCompensationPlansScheduleofSharesIssuedNetofSharesCanceledExpiredDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/StockBasedCompensationPlansScheduleofSharesIssuedNetofSharesCanceledExpiredDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5f98773b-edc2-4194-a152-4c17adf2dd65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a7cde88d-382c-47b2-9195-8c07ba9b6fd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5f98773b-edc2-4194-a152-4c17adf2dd65" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a7cde88d-382c-47b2-9195-8c07ba9b6fd6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_34a2be53-47a5-41c1-87aa-92e96e665ae0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a7cde88d-382c-47b2-9195-8c07ba9b6fd6" xlink:to="loc_us-gaap_PlanNameAxis_34a2be53-47a5-41c1-87aa-92e96e665ae0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_34a2be53-47a5-41c1-87aa-92e96e665ae0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_34a2be53-47a5-41c1-87aa-92e96e665ae0" xlink:to="loc_us-gaap_PlanNameDomain_34a2be53-47a5-41c1-87aa-92e96e665ae0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_bcf78581-aabb-4b99-9433-28eb3e8ea9ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_34a2be53-47a5-41c1-87aa-92e96e665ae0" xlink:to="loc_us-gaap_PlanNameDomain_bcf78581-aabb-4b99-9433-28eb3e8ea9ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_A2019OmnibusIncentivePlanMember_f2912e1e-1093-454b-9a6c-111b68518dc3" xlink:href="gntx-20260331.xsd#gntx_A2019OmnibusIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_bcf78581-aabb-4b99-9433-28eb3e8ea9ff" xlink:to="loc_gntx_A2019OmnibusIncentivePlanMember_f2912e1e-1093-454b-9a6c-111b68518dc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_9d82e811-fea5-48f7-9245-f4a209924606" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a7cde88d-382c-47b2-9195-8c07ba9b6fd6" xlink:to="loc_us-gaap_AwardTypeAxis_9d82e811-fea5-48f7-9245-f4a209924606" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9d82e811-fea5-48f7-9245-f4a209924606_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_9d82e811-fea5-48f7-9245-f4a209924606" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9d82e811-fea5-48f7-9245-f4a209924606_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0aa59eb6-1653-4b24-bd3a-fde9e370eb72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_9d82e811-fea5-48f7-9245-f4a209924606" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0aa59eb6-1653-4b24-bd3a-fde9e370eb72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_NonQualifiedStockOptionMember_0324aa96-42d6-46c3-b0bb-3bb6dee2e9ec" xlink:href="gntx-20260331.xsd#gntx_NonQualifiedStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0aa59eb6-1653-4b24-bd3a-fde9e370eb72" xlink:to="loc_gntx_NonQualifiedStockOptionMember_0324aa96-42d6-46c3-b0bb-3bb6dee2e9ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_56290b0d-2a38-49b0-96c0-0b14ba135518" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0aa59eb6-1653-4b24-bd3a-fde9e370eb72" xlink:to="loc_us-gaap_RestrictedStockMember_56290b0d-2a38-49b0-96c0-0b14ba135518" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_addd2339-4493-4c98-a26a-afc329a5576e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0aa59eb6-1653-4b24-bd3a-fde9e370eb72" xlink:to="loc_us-gaap_PerformanceSharesMember_addd2339-4493-4c98-a26a-afc329a5576e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_3919f47a-62c9-4233-93c8-c10cf3b913e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5f98773b-edc2-4194-a152-4c17adf2dd65" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_3919f47a-62c9-4233-93c8-c10cf3b913e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_a28a1ebd-fcf8-410e-af6c-b8a013df9499" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5f98773b-edc2-4194-a152-4c17adf2dd65" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_a28a1ebd-fcf8-410e-af6c-b8a013df9499" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod_aeb395d2-96b1-4b76-b78b-90d6a14069fd" xlink:href="gntx-20260331.xsd#gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5f98773b-edc2-4194-a152-4c17adf2dd65" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod_aeb395d2-96b1-4b76-b78b-90d6a14069fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConversionRate_163b677e-1c5c-4030-ab69-c628e6256149" xlink:href="gntx-20260331.xsd#gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5f98773b-edc2-4194-a152-4c17adf2dd65" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConversionRate_163b677e-1c5c-4030-ab69-c628e6256149" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentConversionRate_f5f6f7b7-7456-4188-a946-f22421fe765d" xlink:href="gntx-20260331.xsd#gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5f98773b-edc2-4194-a152-4c17adf2dd65" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentConversionRate_f5f6f7b7-7456-4188-a946-f22421fe765d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_61653227-b60f-4d42-a23c-0013d6698584" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5f98773b-edc2-4194-a152-4c17adf2dd65" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_61653227-b60f-4d42-a23c-0013d6698584" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/ComprehensiveIncomeLossScheduleofAOCIDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#ComprehensiveIncomeLossScheduleofAOCIDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/ComprehensiveIncomeLossScheduleofAOCIDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_53f62807-f152-4d1c-bbd4-46b88db83849" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_4fd8f782-a2b7-4e9f-8261-13647a967cfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_53f62807-f152-4d1c-bbd4-46b88db83849" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_4fd8f782-a2b7-4e9f-8261-13647a967cfa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_38193aba-b086-48d3-8d15-927c14821e35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_4fd8f782-a2b7-4e9f-8261-13647a967cfa" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_38193aba-b086-48d3-8d15-927c14821e35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_38193aba-b086-48d3-8d15-927c14821e35_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_38193aba-b086-48d3-8d15-927c14821e35" xlink:to="loc_us-gaap_EquityComponentDomain_38193aba-b086-48d3-8d15-927c14821e35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_b5156336-7333-4c5d-af4f-56cc191dc860" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_38193aba-b086-48d3-8d15-927c14821e35" xlink:to="loc_us-gaap_EquityComponentDomain_b5156336-7333-4c5d-af4f-56cc191dc860" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d1bec1f6-eb7b-4531-92df-1cdffbc086d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b5156336-7333-4c5d-af4f-56cc191dc860" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d1bec1f6-eb7b-4531-92df-1cdffbc086d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_5148df7d-c333-4f62-805d-0439177020fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d1bec1f6-eb7b-4531-92df-1cdffbc086d3" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_5148df7d-c333-4f62-805d-0439177020fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_42ddb50d-48ea-41ac-858f-41c4f4b29a27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d1bec1f6-eb7b-4531-92df-1cdffbc086d3" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_42ddb50d-48ea-41ac-858f-41c4f4b29a27" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_b93f2c84-6aa4-4486-bb88-855e266815d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d1bec1f6-eb7b-4531-92df-1cdffbc086d3" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_b93f2c84-6aa4-4486-bb88-855e266815d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_20029322-ecd5-4945-89d3-953ff0db3107" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_53f62807-f152-4d1c-bbd4-46b88db83849" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_20029322-ecd5-4945-89d3-953ff0db3107" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_6419c140-d444-4e46-b2ae-ebe41af4f9de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_20029322-ecd5-4945-89d3-953ff0db3107" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_6419c140-d444-4e46-b2ae-ebe41af4f9de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_d1646338-90f1-4eb6-b149-4cbedcfc26fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_20029322-ecd5-4945-89d3-953ff0db3107" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_d1646338-90f1-4eb6-b149-4cbedcfc26fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_604b4242-b9bc-4fe4-961d-dea6b6c79c9d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_20029322-ecd5-4945-89d3-953ff0db3107" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_604b4242-b9bc-4fe4-961d-dea6b6c79c9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_d521af42-7fb2-472f-9d89-c0584e0a84e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_20029322-ecd5-4945-89d3-953ff0db3107" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_d521af42-7fb2-472f-9d89-c0584e0a84e9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_24cfa664-35ac-4127-8e2e-eb681e5281c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/ComprehensiveIncomeLossScheduleofReclassificationsOutofAccumulatedOtherComprehensiveLossDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#ComprehensiveIncomeLossScheduleofReclassificationsOutofAccumulatedOtherComprehensiveLossDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/ComprehensiveIncomeLossScheduleofReclassificationsOutofAccumulatedOtherComprehensiveLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_4f451ef3-59cd-45fa-9f3d-8a6b6ec674f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_05081711-d507-4644-9b0c-faae59b21feb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_4f451ef3-59cd-45fa-9f3d-8a6b6ec674f9" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_05081711-d507-4644-9b0c-faae59b21feb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_a711925a-e6cc-4731-9eb9-8e98259427ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_05081711-d507-4644-9b0c-faae59b21feb" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_a711925a-e6cc-4731-9eb9-8e98259427ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_a711925a-e6cc-4731-9eb9-8e98259427ab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_a711925a-e6cc-4731-9eb9-8e98259427ab" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_a711925a-e6cc-4731-9eb9-8e98259427ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_9998f626-084b-47c9-b8af-127261ba9eba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_a711925a-e6cc-4731-9eb9-8e98259427ab" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_9998f626-084b-47c9-b8af-127261ba9eba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_411253ae-783c-4de3-8700-b0d7ed24e932" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_9998f626-084b-47c9-b8af-127261ba9eba" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_411253ae-783c-4de3-8700-b0d7ed24e932" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_8fb51c87-9fed-434e-ad88-6ae0b6e82ac4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_05081711-d507-4644-9b0c-faae59b21feb" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_8fb51c87-9fed-434e-ad88-6ae0b6e82ac4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8fb51c87-9fed-434e-ad88-6ae0b6e82ac4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8fb51c87-9fed-434e-ad88-6ae0b6e82ac4" xlink:to="loc_us-gaap_EquityComponentDomain_8fb51c87-9fed-434e-ad88-6ae0b6e82ac4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_576b20e8-2c7d-4ee9-aff5-f24c32bf1013" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8fb51c87-9fed-434e-ad88-6ae0b6e82ac4" xlink:to="loc_us-gaap_EquityComponentDomain_576b20e8-2c7d-4ee9-aff5-f24c32bf1013" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_d50b03fa-359e-42ed-8fe2-ff6d022f57f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_576b20e8-2c7d-4ee9-aff5-f24c32bf1013" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_d50b03fa-359e-42ed-8fe2-ff6d022f57f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_fade76f2-15f6-4850-bdab-4c244626e797" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_576b20e8-2c7d-4ee9-aff5-f24c32bf1013" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_fade76f2-15f6-4850-bdab-4c244626e797" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_209ecae5-d1a1-420b-93e7-161f77a6d66b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_4f451ef3-59cd-45fa-9f3d-8a6b6ec674f9" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_209ecae5-d1a1-420b-93e7-161f77a6d66b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_865ca0a2-45a5-4712-88c8-c9e61e465c11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_4f451ef3-59cd-45fa-9f3d-8a6b6ec674f9" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_865ca0a2-45a5-4712-88c8-c9e61e465c11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_6be4d861-1b69-417f-8bd9-a55162b413c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_4f451ef3-59cd-45fa-9f3d-8a6b6ec674f9" xlink:to="loc_us-gaap_ProfitLoss_6be4d861-1b69-417f-8bd9-a55162b413c6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/DebtandFinancingArrangementsDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#DebtandFinancingArrangementsDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/DebtandFinancingArrangementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_0587fdad-847f-4788-a30a-a2b3d8486c05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_4a14b5ab-eb48-408a-95c3-29d15cc2c046" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0587fdad-847f-4788-a30a-a2b3d8486c05" xlink:to="loc_us-gaap_DebtInstrumentTable_4a14b5ab-eb48-408a-95c3-29d15cc2c046" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_12f8ff0d-f1a5-46c8-85ed-57ec2da6f4ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_4a14b5ab-eb48-408a-95c3-29d15cc2c046" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_12f8ff0d-f1a5-46c8-85ed-57ec2da6f4ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_12f8ff0d-f1a5-46c8-85ed-57ec2da6f4ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_12f8ff0d-f1a5-46c8-85ed-57ec2da6f4ad" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_12f8ff0d-f1a5-46c8-85ed-57ec2da6f4ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_8c5b6564-d0ab-4ec4-b6d5-0032b8f7adf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_12f8ff0d-f1a5-46c8-85ed-57ec2da6f4ad" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_8c5b6564-d0ab-4ec4-b6d5-0032b8f7adf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_3cd60453-2e81-4368-a291-ebc41654df13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_8c5b6564-d0ab-4ec4-b6d5-0032b8f7adf7" xlink:to="loc_us-gaap_LineOfCreditMember_3cd60453-2e81-4368-a291-ebc41654df13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_ff5dbe39-8857-40d4-9d56-eb300aee50d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_4a14b5ab-eb48-408a-95c3-29d15cc2c046" xlink:to="loc_us-gaap_CreditFacilityAxis_ff5dbe39-8857-40d4-9d56-eb300aee50d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ff5dbe39-8857-40d4-9d56-eb300aee50d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_ff5dbe39-8857-40d4-9d56-eb300aee50d3" xlink:to="loc_us-gaap_CreditFacilityDomain_ff5dbe39-8857-40d4-9d56-eb300aee50d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_bb470e2a-8668-43c8-98c2-3004dcfecf2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_ff5dbe39-8857-40d4-9d56-eb300aee50d3" xlink:to="loc_us-gaap_CreditFacilityDomain_bb470e2a-8668-43c8-98c2-3004dcfecf2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_d73fec16-e1b3-4dfc-8579-37c0b0a96f26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_bb470e2a-8668-43c8-98c2-3004dcfecf2c" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_d73fec16-e1b3-4dfc-8579-37c0b0a96f26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_6766e248-7226-4b12-a6b5-f2d2aeb50901" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_bb470e2a-8668-43c8-98c2-3004dcfecf2c" xlink:to="loc_us-gaap_LetterOfCreditMember_6766e248-7226-4b12-a6b5-f2d2aeb50901" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_SwingLoansMember_b2f13dd4-c283-44b3-9e09-02191fb767d6" xlink:href="gntx-20260331.xsd#gntx_SwingLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_bb470e2a-8668-43c8-98c2-3004dcfecf2c" xlink:to="loc_gntx_SwingLoansMember_b2f13dd4-c283-44b3-9e09-02191fb767d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_a8012ce9-f540-4bf2-920b-0447243350b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_4a14b5ab-eb48-408a-95c3-29d15cc2c046" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_a8012ce9-f540-4bf2-920b-0447243350b4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_a8012ce9-f540-4bf2-920b-0447243350b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_a8012ce9-f540-4bf2-920b-0447243350b4" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_a8012ce9-f540-4bf2-920b-0447243350b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_505a0571-814d-4b38-80ea-58cb2a3d2e37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_a8012ce9-f540-4bf2-920b-0447243350b4" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_505a0571-814d-4b38-80ea-58cb2a3d2e37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_a5e5b1a9-8965-4b5a-aae8-fc77c5738626" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_505a0571-814d-4b38-80ea-58cb2a3d2e37" xlink:to="loc_us-gaap_SecuredDebtMember_a5e5b1a9-8965-4b5a-aae8-fc77c5738626" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_059622c6-58f1-4be9-b538-b2e3e916a7f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_4a14b5ab-eb48-408a-95c3-29d15cc2c046" xlink:to="loc_us-gaap_DebtInstrumentAxis_059622c6-58f1-4be9-b538-b2e3e916a7f2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_059622c6-58f1-4be9-b538-b2e3e916a7f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_059622c6-58f1-4be9-b538-b2e3e916a7f2" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_059622c6-58f1-4be9-b538-b2e3e916a7f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_5ce42993-25a0-4017-b39f-ab25cf58cd6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_059622c6-58f1-4be9-b538-b2e3e916a7f2" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_5ce42993-25a0-4017-b39f-ab25cf58cd6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareholderLoanAgreementMember_a65ab87b-0008-409e-ac8c-ee9675a32198" xlink:href="gntx-20260331.xsd#gntx_ShareholderLoanAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_5ce42993-25a0-4017-b39f-ab25cf58cd6a" xlink:to="loc_gntx_ShareholderLoanAgreementMember_a65ab87b-0008-409e-ac8c-ee9675a32198" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_feb7f848-f201-4144-bfd5-ef4b5e51493d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0587fdad-847f-4788-a30a-a2b3d8486c05" xlink:to="loc_us-gaap_DebtInstrumentTerm_feb7f848-f201-4144-bfd5-ef4b5e51493d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_2d796a94-68ec-4631-899a-6de69b6164db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0587fdad-847f-4788-a30a-a2b3d8486c05" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_2d796a94-68ec-4631-899a-6de69b6164db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_a18bd1f1-751a-41cc-a649-64b9de71ccbe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0587fdad-847f-4788-a30a-a2b3d8486c05" xlink:to="loc_us-gaap_LongTermDebt_a18bd1f1-751a-41cc-a649-64b9de71ccbe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_26eb1134-fc1e-4318-9650-afea2269643f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0587fdad-847f-4788-a30a-a2b3d8486c05" xlink:to="loc_us-gaap_ShortTermBorrowings_26eb1134-fc1e-4318-9650-afea2269643f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ad09f148-872b-49ef-847c-b1c3f842500f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0587fdad-847f-4788-a30a-a2b3d8486c05" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ad09f148-872b-49ef-847c-b1c3f842500f" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/SegmentReportingScheduleofNetSalesandSignificantExpenseCategoriesIncludedinReportableSegmentOperatingProfitDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#SegmentReportingScheduleofNetSalesandSignificantExpenseCategoriesIncludedinReportableSegmentOperatingProfitDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/SegmentReportingScheduleofNetSalesandSignificantExpenseCategoriesIncludedinReportableSegmentOperatingProfitDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_e1187fa2-d2d9-4731-bbe2-49c49a29adc1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_09e76713-e013-40c0-ae52-193d4f1c0dd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e1187fa2-d2d9-4731-bbe2-49c49a29adc1" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_09e76713-e013-40c0-ae52-193d4f1c0dd5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_a0f1c1e4-4f29-4123-bdc1-b38ed17f07a0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_09e76713-e013-40c0-ae52-193d4f1c0dd5" xlink:to="loc_srt_ConsolidationItemsAxis_a0f1c1e4-4f29-4123-bdc1-b38ed17f07a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_a0f1c1e4-4f29-4123-bdc1-b38ed17f07a0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_a0f1c1e4-4f29-4123-bdc1-b38ed17f07a0" xlink:to="loc_srt_ConsolidationItemsDomain_a0f1c1e4-4f29-4123-bdc1-b38ed17f07a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_7edfbef2-6ea6-41fe-883d-cf74813a3ba7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_a0f1c1e4-4f29-4123-bdc1-b38ed17f07a0" xlink:to="loc_srt_ConsolidationItemsDomain_7edfbef2-6ea6-41fe-883d-cf74813a3ba7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_9ecd848c-f3f6-4b75-bc73-486e59fed47a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_7edfbef2-6ea6-41fe-883d-cf74813a3ba7" xlink:to="loc_us-gaap_OperatingSegmentsMember_9ecd848c-f3f6-4b75-bc73-486e59fed47a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_c383f6d6-a89e-45ff-9783-c7acd238cb4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_7edfbef2-6ea6-41fe-883d-cf74813a3ba7" xlink:to="loc_us-gaap_CorporateNonSegmentMember_c383f6d6-a89e-45ff-9783-c7acd238cb4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_9548f9c5-fa6a-4c42-ac4b-c208ddcf2942" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_09e76713-e013-40c0-ae52-193d4f1c0dd5" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_9548f9c5-fa6a-4c42-ac4b-c208ddcf2942" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_9548f9c5-fa6a-4c42-ac4b-c208ddcf2942_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_9548f9c5-fa6a-4c42-ac4b-c208ddcf2942" xlink:to="loc_us-gaap_SegmentDomain_9548f9c5-fa6a-4c42-ac4b-c208ddcf2942_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_07f51174-990b-42f7-aceb-c227d82c9076" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_9548f9c5-fa6a-4c42-ac4b-c208ddcf2942" xlink:to="loc_us-gaap_SegmentDomain_07f51174-990b-42f7-aceb-c227d82c9076" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AutomotiveProductsSegmentMember_cc3c25e6-305f-460d-b57a-67f63145f500" xlink:href="gntx-20260331.xsd#gntx_AutomotiveProductsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_07f51174-990b-42f7-aceb-c227d82c9076" xlink:to="loc_gntx_AutomotiveProductsSegmentMember_cc3c25e6-305f-460d-b57a-67f63145f500" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PremiumAudioProductsSegmentMember_75362028-e1f8-4636-9b20-e9aa1eb11c09" xlink:href="gntx-20260331.xsd#gntx_PremiumAudioProductsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_07f51174-990b-42f7-aceb-c227d82c9076" xlink:to="loc_gntx_PremiumAudioProductsSegmentMember_75362028-e1f8-4636-9b20-e9aa1eb11c09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherSegmentsMember_c43b80f4-e6bd-4227-a92a-095d49c60ea5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllOtherSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_07f51174-990b-42f7-aceb-c227d82c9076" xlink:to="loc_us-gaap_AllOtherSegmentsMember_c43b80f4-e6bd-4227-a92a-095d49c60ea5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_878d66b8-d006-4157-b6c3-fef28d69e623" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e1187fa2-d2d9-4731-bbe2-49c49a29adc1" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_878d66b8-d006-4157-b6c3-fef28d69e623" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_913a086a-de95-455e-af6a-f1d58201668a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e1187fa2-d2d9-4731-bbe2-49c49a29adc1" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_913a086a-de95-455e-af6a-f1d58201668a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_684d27db-dfb4-4aea-a43a-e191aed9cd1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e1187fa2-d2d9-4731-bbe2-49c49a29adc1" xlink:to="loc_us-gaap_OperatingExpenses_684d27db-dfb4-4aea-a43a-e191aed9cd1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_c88b694b-87b2-4a98-834c-048726ed2800" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e1187fa2-d2d9-4731-bbe2-49c49a29adc1" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_c88b694b-87b2-4a98-834c-048726ed2800" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_fefcde99-190b-431e-8a98-23290851e2ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e1187fa2-d2d9-4731-bbe2-49c49a29adc1" xlink:to="loc_us-gaap_OperatingIncomeLoss_fefcde99-190b-431e-8a98-23290851e2ec" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/RevenueScheduleofDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#RevenueScheduleofDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/RevenueScheduleofDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_eaafc8a6-5230-4351-82f5-b66233ff3049" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_f8c8c917-1f76-44d9-a168-fe980298ea8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_eaafc8a6-5230-4351-82f5-b66233ff3049" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_f8c8c917-1f76-44d9-a168-fe980298ea8a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_3a4f032e-1ad0-4769-b7c3-701f2b9a1918" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f8c8c917-1f76-44d9-a168-fe980298ea8a" xlink:to="loc_srt_StatementGeographicalAxis_3a4f032e-1ad0-4769-b7c3-701f2b9a1918" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_3a4f032e-1ad0-4769-b7c3-701f2b9a1918_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_3a4f032e-1ad0-4769-b7c3-701f2b9a1918" xlink:to="loc_srt_SegmentGeographicalDomain_3a4f032e-1ad0-4769-b7c3-701f2b9a1918_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_3a4f032e-1ad0-4769-b7c3-701f2b9a1918" xlink:to="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_644d5025-48a0-4e88-b5c6-fa50046414f8" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:to="loc_country_US_644d5025-48a0-4e88-b5c6-fa50046414f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_JP_bd88204c-e4d5-4396-beca-ada1dabc038c" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_JP"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:to="loc_country_JP_bd88204c-e4d5-4396-beca-ada1dabc038c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_51f58f3e-41a5-4288-b474-b94d3f7751e5" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:to="loc_country_DE_51f58f3e-41a5-4288-b474-b94d3f7751e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_KR_a30fd127-460c-4025-80e5-7074c1a52d0f" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_KR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:to="loc_country_KR_a30fd127-460c-4025-80e5-7074c1a52d0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_MX_2c6efb14-e7a2-410a-b9d8-73ca6fe2c3cd" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_MX"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:to="loc_country_MX_2c6efb14-e7a2-410a-b9d8-73ca6fe2c3cd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_b3bbc224-673b-4c87-9235-6f999129011f" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:to="loc_country_CN_b3bbc224-673b-4c87-9235-6f999129011f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OtherCountriesMember_4dfd2c5c-1e29-4b71-a9b1-aea263de54ed" xlink:href="gntx-20260331.xsd#gntx_OtherCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_3bf8aef6-0665-42f9-a764-68c73822a944" xlink:to="loc_gntx_OtherCountriesMember_4dfd2c5c-1e29-4b71-a9b1-aea263de54ed" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_f08a3cdc-d5d2-4c2b-999a-82e7828121dc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f8c8c917-1f76-44d9-a168-fe980298ea8a" xlink:to="loc_srt_ProductOrServiceAxis_f08a3cdc-d5d2-4c2b-999a-82e7828121dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_f08a3cdc-d5d2-4c2b-999a-82e7828121dc_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_f08a3cdc-d5d2-4c2b-999a-82e7828121dc" xlink:to="loc_srt_ProductsAndServicesDomain_f08a3cdc-d5d2-4c2b-999a-82e7828121dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ba2e692c-d343-4b53-8074-b200deb9381f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_f08a3cdc-d5d2-4c2b-999a-82e7828121dc" xlink:to="loc_srt_ProductsAndServicesDomain_ba2e692c-d343-4b53-8074-b200deb9381f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AutomotiveProductsMember_0c41e80e-ef90-4cf1-92d2-8cdd8cc4a3e9" xlink:href="gntx-20260331.xsd#gntx_AutomotiveProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ba2e692c-d343-4b53-8074-b200deb9381f" xlink:to="loc_gntx_AutomotiveProductsMember_0c41e80e-ef90-4cf1-92d2-8cdd8cc4a3e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AutomotiveMirrorsElectronicsMember_4afcd574-22ee-450f-95bb-41c956babc9d" xlink:href="gntx-20260331.xsd#gntx_AutomotiveMirrorsElectronicsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_AutomotiveProductsMember_0c41e80e-ef90-4cf1-92d2-8cdd8cc4a3e9" xlink:to="loc_gntx_AutomotiveMirrorsElectronicsMember_4afcd574-22ee-450f-95bb-41c956babc9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_HomeLinkModulesMember_e66ad5fd-0ae6-42fe-8401-f88cc81fcb8d" xlink:href="gntx-20260331.xsd#gntx_HomeLinkModulesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_AutomotiveProductsMember_0c41e80e-ef90-4cf1-92d2-8cdd8cc4a3e9" xlink:to="loc_gntx_HomeLinkModulesMember_e66ad5fd-0ae6-42fe-8401-f88cc81fcb8d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PremiumAudioProductsMember_ba300778-b814-4180-b0d4-d2b26fa75319" xlink:href="gntx-20260331.xsd#gntx_PremiumAudioProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ba2e692c-d343-4b53-8074-b200deb9381f" xlink:to="loc_gntx_PremiumAudioProductsMember_ba300778-b814-4180-b0d4-d2b26fa75319" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PremiumSpeakerProductsMember_ec0adb66-21c2-4d7f-9941-9a08068713a4" xlink:href="gntx-20260331.xsd#gntx_PremiumSpeakerProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_PremiumAudioProductsMember_ba300778-b814-4180-b0d4-d2b26fa75319" xlink:to="loc_gntx_PremiumSpeakerProductsMember_ec0adb66-21c2-4d7f-9941-9a08068713a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PremiumReceiverProductsMember_bdf4b6e5-323d-4cc4-b3a0-e2157a8fdaf0" xlink:href="gntx-20260331.xsd#gntx_PremiumReceiverProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_PremiumAudioProductsMember_ba300778-b814-4180-b0d4-d2b26fa75319" xlink:to="loc_gntx_PremiumReceiverProductsMember_bdf4b6e5-323d-4cc4-b3a0-e2157a8fdaf0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OtherProductsMember_7d936fcb-9f8c-4e41-8d81-cf2e7d61a93d" xlink:href="gntx-20260331.xsd#gntx_OtherProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ba2e692c-d343-4b53-8074-b200deb9381f" xlink:to="loc_gntx_OtherProductsMember_7d936fcb-9f8c-4e41-8d81-cf2e7d61a93d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_FireProtectionProductsMember_0e9867ce-a524-4a8b-9a34-e1737349aa0a" xlink:href="gntx-20260331.xsd#gntx_FireProtectionProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_OtherProductsMember_7d936fcb-9f8c-4e41-8d81-cf2e7d61a93d" xlink:to="loc_gntx_FireProtectionProductsMember_0e9867ce-a524-4a8b-9a34-e1737349aa0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_WindowsProductMember_d4fb4a08-0047-42f6-9575-3136ad9b98f8" xlink:href="gntx-20260331.xsd#gntx_WindowsProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_OtherProductsMember_7d936fcb-9f8c-4e41-8d81-cf2e7d61a93d" xlink:to="loc_gntx_WindowsProductMember_d4fb4a08-0047-42f6-9575-3136ad9b98f8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_MedicalProductsMember_26d0e8fa-8391-47ab-8631-6f42e916c84a" xlink:href="gntx-20260331.xsd#gntx_MedicalProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_OtherProductsMember_7d936fcb-9f8c-4e41-8d81-cf2e7d61a93d" xlink:to="loc_gntx_MedicalProductsMember_26d0e8fa-8391-47ab-8631-6f42e916c84a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AftermarketProductsMember_5a44d7f3-05e6-4335-a67f-21581770ee56" xlink:href="gntx-20260331.xsd#gntx_AftermarketProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_OtherProductsMember_7d936fcb-9f8c-4e41-8d81-cf2e7d61a93d" xlink:to="loc_gntx_AftermarketProductsMember_5a44d7f3-05e6-4335-a67f-21581770ee56" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ConsumerElectronicProductsMember_8cd2ec28-62e2-416f-861b-5a13ea904d56" xlink:href="gntx-20260331.xsd#gntx_ConsumerElectronicProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_OtherProductsMember_7d936fcb-9f8c-4e41-8d81-cf2e7d61a93d" xlink:to="loc_gntx_ConsumerElectronicProductsMember_8cd2ec28-62e2-416f-861b-5a13ea904d56" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BiometricProductsMember_7162e0ab-7ad3-487a-ad5e-58e92c32e8f2" xlink:href="gntx-20260331.xsd#gntx_BiometricProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_OtherProductsMember_7d936fcb-9f8c-4e41-8d81-cf2e7d61a93d" xlink:to="loc_gntx_BiometricProductsMember_7162e0ab-7ad3-487a-ad5e-58e92c32e8f2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_5866048f-8f0e-4fd0-be28-e23a085e19da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_eaafc8a6-5230-4351-82f5-b66233ff3049" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_5866048f-8f0e-4fd0-be28-e23a085e19da" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#LeasesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/LeasesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_6b86038d-200e-4466-b30e-6b3232c833af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_c7b3a69f-32b3-48be-afcd-e8cba0f943df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6b86038d-200e-4466-b30e-6b3232c833af" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_c7b3a69f-32b3-48be-afcd-e8cba0f943df" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_677e91ba-4ef6-40dc-a6dc-e44772f8df15" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_c7b3a69f-32b3-48be-afcd-e8cba0f943df" xlink:to="loc_srt_RangeAxis_677e91ba-4ef6-40dc-a6dc-e44772f8df15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_677e91ba-4ef6-40dc-a6dc-e44772f8df15_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_677e91ba-4ef6-40dc-a6dc-e44772f8df15" xlink:to="loc_srt_RangeMember_677e91ba-4ef6-40dc-a6dc-e44772f8df15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4d2318cd-4625-40a8-bfcb-415d1d109f4b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_677e91ba-4ef6-40dc-a6dc-e44772f8df15" xlink:to="loc_srt_RangeMember_4d2318cd-4625-40a8-bfcb-415d1d109f4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_9ad9f25b-2abe-4d18-bec2-eb9adbbdcc72" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4d2318cd-4625-40a8-bfcb-415d1d109f4b" xlink:to="loc_srt_MinimumMember_9ad9f25b-2abe-4d18-bec2-eb9adbbdcc72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_7ce5c6b3-1924-4660-a371-79ce1a98d7ba" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4d2318cd-4625-40a8-bfcb-415d1d109f4b" xlink:to="loc_srt_MaximumMember_7ce5c6b3-1924-4660-a371-79ce1a98d7ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_00f79215-dc54-4bac-be76-97518b9720fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6b86038d-200e-4466-b30e-6b3232c833af" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_00f79215-dc54-4bac-be76-97518b9720fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_9f8e6c16-ac42-4142-9171-5d97b504c6ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6b86038d-200e-4466-b30e-6b3232c833af" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_9f8e6c16-ac42-4142-9171-5d97b504c6ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_e9620d87-06db-4d44-a819-1db5c2278818" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6b86038d-200e-4466-b30e-6b3232c833af" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_e9620d87-06db-4d44-a819-1db5c2278818" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#AcquisitionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/AcquisitionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_5d90bf54-5416-428a-942c-477e33baf56e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_5d90bf54-5416-428a-942c-477e33baf56e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d6e3e-db60-7e78-9fa5-79fd8ba7689d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_5d90bf54-5416-428a-942c-477e33baf56e" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d6e3e-db60-7e78-9fa5-79fd8ba7689d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d6e3e-db60-7e78-9fa5-79fd8ba7689d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019d6e3e-db60-7e78-9fa5-79fd8ba7689d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d6e3e-db60-7e78-9fa5-79fd8ba7689d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d6e3e-db60-7517-8f07-da71ac971094" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019d6e3e-db60-7e78-9fa5-79fd8ba7689d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d6e3e-db60-7517-8f07-da71ac971094" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BioConnectInc.Member_019d6e3e-db60-7cff-8821-7f4ca36486c2" xlink:href="gntx-20260331.xsd#gntx_BioConnectInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d6e3e-db60-7517-8f07-da71ac971094" xlink:to="loc_gntx_BioConnectInc.Member_019d6e3e-db60-7cff-8821-7f4ca36486c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_VOXXInternationalCorporationMember_019d6e3f-32a7-7b13-8bd0-299e60479395" xlink:href="gntx-20260331.xsd#gntx_VOXXInternationalCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d6e3e-db60-7517-8f07-da71ac971094" xlink:to="loc_gntx_VOXXInternationalCorporationMember_019d6e3f-32a7-7b13-8bd0-299e60479395" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_EyeLockLLCMember_019d6e3f-bdf4-78d1-b4bd-9d533eaf8290" xlink:href="gntx-20260331.xsd#gntx_EyeLockLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d6e3e-db60-7517-8f07-da71ac971094" xlink:to="loc_gntx_EyeLockLLCMember_019d6e3f-bdf4-78d1-b4bd-9d533eaf8290" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_GalvanEyesLLCMember_019d6e3f-bdf4-7b82-b485-025f5c952ed2" xlink:href="gntx-20260331.xsd#gntx_GalvanEyesLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d6e3e-db60-7517-8f07-da71ac971094" xlink:to="loc_gntx_GalvanEyesLLCMember_019d6e3f-bdf4-7b82-b485-025f5c952ed2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019d6e3f-32a7-7fe8-acd3-19ea8112ac74" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_5d90bf54-5416-428a-942c-477e33baf56e" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019d6e3f-32a7-7fe8-acd3-19ea8112ac74" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019d6e3f-32a7-7fe8-acd3-19ea8112ac74_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019d6e3f-32a7-7fe8-acd3-19ea8112ac74" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019d6e3f-32a7-7fe8-acd3-19ea8112ac74_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019d6e3f-32a7-7924-acfc-508b8bb65237" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019d6e3f-32a7-7fe8-acd3-19ea8112ac74" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019d6e3f-32a7-7924-acfc-508b8bb65237" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_VOXXInternationalCorporationMember_019d6e3f-32a7-7837-93a8-3d72a4634fc0" xlink:href="gntx-20260331.xsd#gntx_VOXXInternationalCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019d6e3f-32a7-7924-acfc-508b8bb65237" xlink:to="loc_gntx_VOXXInternationalCorporationMember_019d6e3f-32a7-7837-93a8-3d72a4634fc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019d6e3f-32a7-7f36-b20d-fad28f4786e0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_5d90bf54-5416-428a-942c-477e33baf56e" xlink:to="loc_srt_OwnershipAxis_019d6e3f-32a7-7f36-b20d-fad28f4786e0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019d6e3f-32a7-7f36-b20d-fad28f4786e0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019d6e3f-32a7-7f36-b20d-fad28f4786e0" xlink:to="loc_srt_OwnershipDomain_019d6e3f-32a7-7f36-b20d-fad28f4786e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019d6e3f-32a7-7bfa-9928-fb6441a341fc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019d6e3f-32a7-7f36-b20d-fad28f4786e0" xlink:to="loc_srt_OwnershipDomain_019d6e3f-32a7-7bfa-9928-fb6441a341fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BioCenturionJointVentureMember_019d6e3f-32a7-7873-a096-e6d1fefb6823" xlink:href="gntx-20260331.xsd#gntx_BioCenturionJointVentureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019d6e3f-32a7-7bfa-9928-fb6441a341fc" xlink:to="loc_gntx_BioCenturionJointVentureMember_019d6e3f-32a7-7873-a096-e6d1fefb6823" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OnkyoTechnologyKKJointVentureMember_019d6e3f-9455-7f2e-a944-cfa3275b3e3d" xlink:href="gntx-20260331.xsd#gntx_OnkyoTechnologyKKJointVentureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019d6e3f-32a7-7bfa-9928-fb6441a341fc" xlink:to="loc_gntx_OnkyoTechnologyKKJointVentureMember_019d6e3f-9455-7f2e-a944-cfa3275b3e3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019d6e3f-32a7-794d-91fb-2ca182cd6b07" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_5d90bf54-5416-428a-942c-477e33baf56e" xlink:to="loc_dei_LegalEntityAxis_019d6e3f-32a7-794d-91fb-2ca182cd6b07" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019d6e3f-32a7-794d-91fb-2ca182cd6b07_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019d6e3f-32a7-794d-91fb-2ca182cd6b07" xlink:to="loc_dei_EntityDomain_019d6e3f-32a7-794d-91fb-2ca182cd6b07_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019d6e3f-32a7-72a3-a822-b5ed649d8463" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019d6e3f-32a7-794d-91fb-2ca182cd6b07" xlink:to="loc_dei_EntityDomain_019d6e3f-32a7-72a3-a822-b5ed649d8463" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_EyeLockLLCMember_019d6e3f-32a7-7dbb-a6c3-03c1becf5e67" xlink:href="gntx-20260331.xsd#gntx_EyeLockLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019d6e3f-32a7-72a3-a822-b5ed649d8463" xlink:to="loc_gntx_EyeLockLLCMember_019d6e3f-32a7-7dbb-a6c3-03c1becf5e67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_VOXXInternationalCorporationsPremiumAudioCompanyMember_019d6e3f-9455-7057-9a2e-5baa78a2c0f5" xlink:href="gntx-20260331.xsd#gntx_VOXXInternationalCorporationsPremiumAudioCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019d6e3f-32a7-72a3-a822-b5ed649d8463" xlink:to="loc_gntx_VOXXInternationalCorporationsPremiumAudioCompanyMember_019d6e3f-9455-7057-9a2e-5baa78a2c0f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_SharpCorporationMember_019d6e3f-9455-771f-85a3-c9546651e59a" xlink:href="gntx-20260331.xsd#gntx_SharpCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019d6e3f-32a7-72a3-a822-b5ed649d8463" xlink:to="loc_gntx_SharpCorporationMember_019d6e3f-9455-771f-85a3-c9546651e59a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_GalvanEyesLLCMember_019d6e3f-bdf4-7340-a230-84981280499c" xlink:href="gntx-20260331.xsd#gntx_GalvanEyesLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019d6e3f-32a7-72a3-a822-b5ed649d8463" xlink:to="loc_gntx_GalvanEyesLLCMember_019d6e3f-bdf4-7340-a230-84981280499c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019d6e3e-db60-7b61-abc5-bce34c100f62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019d6e3e-db60-7b61-abc5-bce34c100f62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019d6e3f-0942-7ed6-bc14-576371370eab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019d6e3f-0942-7ed6-bc14-576371370eab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_019d6e3f-0942-7117-ae09-8e80b0710fa4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_019d6e3f-0942-7117-ae09-8e80b0710fa4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_019d6e3f-0942-7e3f-85fa-dfb4ed07d835" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_019d6e3f-0942-7e3f-85fa-dfb4ed07d835" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_019d6e3f-0942-793a-9368-e2fd64f859bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_019d6e3f-0942-793a-9368-e2fd64f859bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019d6e3f-0942-703c-9520-838c6e0c1a40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019d6e3f-0942-703c-9520-838c6e0c1a40" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionSharePrice_019d6e3f-32a7-752b-8871-03010591770c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionSharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_BusinessAcquisitionSharePrice_019d6e3f-32a7-752b-8871-03010591770c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019d6e3f-32a7-7b39-88eb-f4d522b9cfab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019d6e3f-32a7-7b39-88eb-f4d522b9cfab" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_019d6e3f-32a7-7c1c-ac0b-7908164396ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentOwnedBalanceShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_019d6e3f-32a7-7c1c-ac0b-7908164396ec" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019d6e3f-32a7-7cac-8e27-831c85e83bdd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019d6e3f-32a7-7cac-8e27-831c85e83bdd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1_019d6e3f-32a7-7879-b89b-384de40b9488" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1_019d6e3f-32a7-7879-b89b-384de40b9488" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiRealizedGainLoss_019d6e3f-32a7-730b-813b-6efd4dffbe9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_us-gaap_EquitySecuritiesFvNiRealizedGainLoss_019d6e3f-32a7-730b-813b-6efd4dffbe9b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OwnershipInterestInJointVenturePercentage_019d6e3f-32a7-7691-875c-a085e559c342" xlink:href="gntx-20260331.xsd#gntx_OwnershipInterestInJointVenturePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_gntx_OwnershipInterestInJointVenturePercentage_019d6e3f-32a7-7691-875c-a085e559c342" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_VotingEquityInterestInJointVenturePercentage_019d6e3f-9455-7fdc-8a4b-a370801afdad" xlink:href="gntx-20260331.xsd#gntx_VotingEquityInterestInJointVenturePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_468cec9d-b126-47ce-964f-86d8420b16db" xlink:to="loc_gntx_VotingEquityInterestInJointVenturePercentage_019d6e3f-9455-7fdc-8a4b-a370801afdad" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/AcquisitionsScheduleofAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#AcquisitionsScheduleofAssetsAcquiredandLiabilitiesAssumedDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/AcquisitionsScheduleofAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019cdb1e-32b9-7082-8bbb-cd864acaf828" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019cdb1e-32b9-7d6c-b417-fa19e73ea6c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019cdb1e-32b9-7082-8bbb-cd864acaf828" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019cdb1e-32b9-7d6c-b417-fa19e73ea6c6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019cdb1e-32b9-71b9-a436-d487318f41d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019cdb1e-32b9-7d6c-b417-fa19e73ea6c6" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019cdb1e-32b9-71b9-a436-d487318f41d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cdb1e-32b9-71b9-a436-d487318f41d7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019cdb1e-32b9-71b9-a436-d487318f41d7" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cdb1e-32b9-71b9-a436-d487318f41d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cdb1e-32b9-7c86-a55f-184c5c0971d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019cdb1e-32b9-71b9-a436-d487318f41d7" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cdb1e-32b9-7c86-a55f-184c5c0971d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BioConnectInc.Member_019cdb1e-32b9-717b-86b2-e6f065a292f1" xlink:href="gntx-20260331.xsd#gntx_BioConnectInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cdb1e-32b9-7c86-a55f-184c5c0971d5" xlink:to="loc_gntx_BioConnectInc.Member_019cdb1e-32b9-717b-86b2-e6f065a292f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_VOXXInternationalCorporationMember_019cdb1e-32b9-75be-8353-b75c8ac705b2" xlink:href="gntx-20260331.xsd#gntx_VOXXInternationalCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cdb1e-32b9-7c86-a55f-184c5c0971d5" xlink:to="loc_gntx_VOXXInternationalCorporationMember_019cdb1e-32b9-75be-8353-b75c8ac705b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdb1e-32b9-72af-8e6a-e273b8d95eab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019cdb1e-32b9-7d6c-b417-fa19e73ea6c6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdb1e-32b9-72af-8e6a-e273b8d95eab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdb1e-32b9-72af-8e6a-e273b8d95eab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdb1e-32b9-72af-8e6a-e273b8d95eab" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdb1e-32b9-72af-8e6a-e273b8d95eab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdb1e-32b9-767d-bef6-0822a85ee2e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cdb1e-32b9-72af-8e6a-e273b8d95eab" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdb1e-32b9-767d-bef6-0822a85ee2e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_019cdb1e-32b9-7369-9c8f-eead77bc340b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdb1e-32b9-767d-bef6-0822a85ee2e0" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_019cdb1e-32b9-7369-9c8f-eead77bc340b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019cdb1e-32b9-71f0-b277-d8374e19f003" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdb1e-32b9-767d-bef6-0822a85ee2e0" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019cdb1e-32b9-71f0-b277-d8374e19f003" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019cdb1e-32b9-754f-984a-e31ad205fd31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cdb1e-32b9-767d-bef6-0822a85ee2e0" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019cdb1e-32b9-754f-984a-e31ad205fd31" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsAbstract_019cdb1e-32b9-70e4-aa25-e45e927dd067" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019cdb1e-32b9-7082-8bbb-cd864acaf828" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsAbstract_019cdb1e-32b9-70e4-aa25-e45e927dd067" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019cdb1e-32b9-7c65-ad08-3f6d84a8d6aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsAbstract_019cdb1e-32b9-70e4-aa25-e45e927dd067" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019cdb1e-32b9-7c65-ad08-3f6d84a8d6aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAcquiredFromAcquisition_019cdb1e-32b9-7347-9f83-2e9aef9b36a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAcquiredFromAcquisition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsAbstract_019cdb1e-32b9-70e4-aa25-e45e927dd067" xlink:to="loc_us-gaap_CashAcquiredFromAcquisition_019cdb1e-32b9-7347-9f83-2e9aef9b36a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019cdb1e-32b9-720c-83cb-63714e5bb301" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsAbstract_019cdb1e-32b9-70e4-aa25-e45e927dd067" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_019cdb1e-32b9-720c-83cb-63714e5bb301" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1_019cdb1e-32b9-7590-8f7c-2eff158ff83b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsAbstract_019cdb1e-32b9-70e4-aa25-e45e927dd067" xlink:to="loc_us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1_019cdb1e-32b9-7590-8f7c-2eff158ff83b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombination1_019cdb1e-32b9-7903-9146-fe862336a7f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombination1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsAbstract_019cdb1e-32b9-70e4-aa25-e45e927dd067" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombination1_019cdb1e-32b9-7903-9146-fe862336a7f7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_019cdb1e-32b9-7b31-90d2-ff305dbc737e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019cdb1e-32b9-7082-8bbb-cd864acaf828" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_019cdb1e-32b9-7b31-90d2-ff305dbc737e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_019cdb1e-32b9-7b31-90d2-ff305dbc737e" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019cdb1e-32b9-798f-87d1-a5694dd4bc89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019cdb1e-32b9-798f-87d1-a5694dd4bc89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019cdb1e-32b9-7cf0-b830-4909ebea22da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019cdb1e-32b9-7cf0-b830-4909ebea22da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019cdb1e-32b9-73da-9373-fc3f4352afed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019cdb1e-32b9-73da-9373-fc3f4352afed" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationRecognizedAssetsAcquiredIncomeTaxRecoverable_019cdb1e-32b9-7187-a8bf-109d7097914d" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationRecognizedAssetsAcquiredIncomeTaxRecoverable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_gntx_BusinessCombinationRecognizedAssetsAcquiredIncomeTaxRecoverable_019cdb1e-32b9-7187-a8bf-109d7097914d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019cdb1e-32b9-77e7-91be-4ce322fa852d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019cdb1e-32b9-77e7-91be-4ce322fa852d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019cdb1e-32b9-7797-a664-59c57750ca43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019cdb1e-32b9-7797-a664-59c57750ca43" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationRecognizedAssetsAcquiredInvestmentInEquitySecurities_019cdb1e-32b9-76e7-805b-5f499c7c201f" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationRecognizedAssetsAcquiredInvestmentInEquitySecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_gntx_BusinessCombinationRecognizedAssetsAcquiredInvestmentInEquitySecurities_019cdb1e-32b9-76e7-805b-5f499c7c201f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019cdb1e-32b9-7813-aab8-ce59aeae8ffe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_us-gaap_Goodwill_019cdb1e-32b9-7813-aab8-ce59aeae8ffe" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_019cdb1e-32b9-7435-ab67-acac84b8f12e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_019cdb1e-32b9-7435-ab67-acac84b8f12e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationRecognizedAssetsAcquiredOperatingLeaseRightOfUseAsset_019cdb1e-32b9-7324-8ad6-58a502ea74c7" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationRecognizedAssetsAcquiredOperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_gntx_BusinessCombinationRecognizedAssetsAcquiredOperatingLeaseRightOfUseAsset_019cdb1e-32b9-7324-8ad6-58a502ea74c7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019cdb1e-32b9-7367-80d8-bd8ccb5384bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019cdb1e-32b9-7367-80d8-bd8ccb5384bb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationRecognizedAssetAcquiredAssetIncludingGoodwill_019cdb1e-32b9-71e6-b6b9-91db9c7e8c54" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationRecognizedAssetAcquiredAssetIncludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019cdb1e-32b9-70d7-ac36-adbc240769f2" xlink:to="loc_gntx_BusinessCombinationRecognizedAssetAcquiredAssetIncludingGoodwill_019cdb1e-32b9-71e6-b6b9-91db9c7e8c54" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_019cdb1e-32b9-7b31-90d2-ff305dbc737e" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019cdb1e-32b9-766f-ae1b-46a281c6f79b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019cdb1e-32b9-766f-ae1b-46a281c6f79b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationRecognizedLiabilitiesAssumedAccruedExpensesAndOtherLiabilityCurrent_019cdb1e-32b9-709e-849b-acb2d9db1c08" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationRecognizedLiabilitiesAssumedAccruedExpensesAndOtherLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:to="loc_gntx_BusinessCombinationRecognizedLiabilitiesAssumedAccruedExpensesAndOtherLiabilityCurrent_019cdb1e-32b9-709e-849b-acb2d9db1c08" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationLiabilitiesAssumedIncomeTaxesPayable_019cdb1e-32b9-72db-ad05-6be62f522033" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationLiabilitiesAssumedIncomeTaxesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:to="loc_gntx_BusinessCombinationLiabilitiesAssumedIncomeTaxesPayable_019cdb1e-32b9-72db-ad05-6be62f522033" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationRecognizedLiabilityAssumedShortTermDebt_019cdb1e-32b9-7fb9-aabb-7c159bb004f5" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationRecognizedLiabilityAssumedShortTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:to="loc_gntx_BusinessCombinationRecognizedLiabilityAssumedShortTermDebt_019cdb1e-32b9-7fb9-aabb-7c159bb004f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019cdb1e-32b9-7b7a-8553-7366fed745f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019cdb1e-32b9-7b7a-8553-7366fed745f9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationLiabilitiesAssumedOperatingLeaseLiability_019cdb1e-32b9-7271-8526-f5df494874e6" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationLiabilitiesAssumedOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:to="loc_gntx_BusinessCombinationLiabilitiesAssumedOperatingLeaseLiability_019cdb1e-32b9-7271-8526-f5df494874e6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities_019cdb1e-32b9-70e8-9af2-1b8e7237f309" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities_019cdb1e-32b9-70e8-9af2-1b8e7237f309" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_019cdb1e-32b9-71f2-bfcf-10a91f297095" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019cdb1e-32b9-746a-8736-a0f9541a635f" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_019cdb1e-32b9-71f2-bfcf-10a91f297095" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_019cdb1e-32b9-7b31-90d2-ff305dbc737e" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPrepaidExpenseAndOtherAssetCurrent_019cdb1e-32b9-7f41-b1c6-45d89400f6b9" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPrepaidExpenseAndOtherAssetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPrepaidExpenseAndOtherAssetCurrent_019cdb1e-32b9-7f41-b1c6-45d89400f6b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIncomeTaxRecoverable_019cdb1e-32b9-7604-a8e4-8b3d716306c7" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIncomeTaxRecoverable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIncomeTaxRecoverable_019cdb1e-32b9-7604-a8e4-8b3d716306c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles_019cdb1e-32b9-7fc9-9b72-2e5f1b54f7ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles_019cdb1e-32b9-7fc9-9b72-2e5f1b54f7ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019cdb1e-32b9-7359-8cd5-468de0cbacff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_019cdb1e-32b9-7359-8cd5-468de0cbacff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxAsset_019cdb1e-32b9-748f-aafe-818e9909d239" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxAsset_019cdb1e-32b9-748f-aafe-818e9909d239" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetIncludingGoodwill_019cdb1e-32b9-71fc-bced-154de0423d8b" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetIncludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetIncludingGoodwill_019cdb1e-32b9-71fc-bced-154de0423d8b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsPayableCurrent_019cdb1e-32b9-74ab-8f91-10bfe2841911" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsPayableCurrent_019cdb1e-32b9-74ab-8f91-10bfe2841911" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpensesAndOtherLiabilityCurrent_019cdb1e-32b9-77ac-a75c-5fbfd0869396" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpensesAndOtherLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpensesAndOtherLiabilityCurrent_019cdb1e-32b9-77ac-a75c-5fbfd0869396" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIncomeTaxPayable_019cdb1e-32b9-7926-9f0e-5008e60df80d" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIncomeTaxPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIncomeTaxPayable_019cdb1e-32b9-7926-9f0e-5008e60df80d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentLiability_019cdb1e-32b9-7144-8448-8f2d504ab061" xlink:href="gntx-20260331.xsd#gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_gntx_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentLiability_019cdb1e-32b9-7144-8448-8f2d504ab061" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_019cdb1e-32b9-7e6f-abc2-569108322eab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_019cdb1e-32b9-739d-b9e1-007c6a465dc1" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_019cdb1e-32b9-7e6f-abc2-569108322eab" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue_019cdb1e-32b9-7560-ad89-29f0f07cbc0a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_019cdb1e-32b9-7b31-90d2-ff305dbc737e" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue_019cdb1e-32b9-7560-ad89-29f0f07cbc0a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterest_019cdb1e-32b9-7a6b-aa1b-4ec8e5583b09" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract_019cdb1e-32b9-7b31-90d2-ff305dbc737e" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterest_019cdb1e-32b9-7a6b-aa1b-4ec8e5583b09" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/AcquisitionsScheduleofRedeemableNoncontrollingInterestDetails" xlink:type="simple" xlink:href="gntx-20260331.xsd#AcquisitionsScheduleofRedeemableNoncontrollingInterestDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/AcquisitionsScheduleofRedeemableNoncontrollingInterestDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_131640ef-772c-4266-98a0-fb895e7ef697" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedeemableNoncontrollingInterestLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable_900d002c-d5a4-4dbb-8b3c-d5ad6fc968c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_131640ef-772c-4266-98a0-fb895e7ef697" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable_900d002c-d5a4-4dbb-8b3c-d5ad6fc968c4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_a7000e28-33fe-43fa-9992-a93711b16898" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable_900d002c-d5a4-4dbb-8b3c-d5ad6fc968c4" xlink:to="loc_srt_OwnershipAxis_a7000e28-33fe-43fa-9992-a93711b16898" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_a7000e28-33fe-43fa-9992-a93711b16898_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_a7000e28-33fe-43fa-9992-a93711b16898" xlink:to="loc_srt_OwnershipDomain_a7000e28-33fe-43fa-9992-a93711b16898_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_b702b232-44b6-49e6-8ae2-9a3cbb931fc1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_a7000e28-33fe-43fa-9992-a93711b16898" xlink:to="loc_srt_OwnershipDomain_b702b232-44b6-49e6-8ae2-9a3cbb931fc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OnkyoTechnologyKKJointVentureMember_395561ca-665f-4230-afad-a9dea9eb83be" xlink:href="gntx-20260331.xsd#gntx_OnkyoTechnologyKKJointVentureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_b702b232-44b6-49e6-8ae2-9a3cbb931fc1" xlink:to="loc_gntx_OnkyoTechnologyKKJointVentureMember_395561ca-665f-4230-afad-a9dea9eb83be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_RedeemableNoncontrollingInterestRollForward_1a7dbe8d-98bb-4632-ad47-0cc32c1e9e0b" xlink:href="gntx-20260331.xsd#gntx_RedeemableNoncontrollingInterestRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_131640ef-772c-4266-98a0-fb895e7ef697" xlink:to="loc_gntx_RedeemableNoncontrollingInterestRollForward_1a7dbe8d-98bb-4632-ad47-0cc32c1e9e0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_648e952f-e803-4bac-8233-6e55a928ffab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_RedeemableNoncontrollingInterestRollForward_1a7dbe8d-98bb-4632-ad47-0cc32c1e9e0b" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_648e952f-e803-4bac-8233-6e55a928ffab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_ef40def1-6c54-4018-9306-cdaf9e59b86d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_RedeemableNoncontrollingInterestRollForward_1a7dbe8d-98bb-4632-ad47-0cc32c1e9e0b" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_ef40def1-6c54-4018-9306-cdaf9e59b86d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_82bff983-7876-4494-9cf7-9e0df35d742d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_RedeemableNoncontrollingInterestRollForward_1a7dbe8d-98bb-4632-ad47-0cc32c1e9e0b" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_82bff983-7876-4494-9cf7-9e0df35d742d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToNoncontrollingInterest_742c1f25-8f3f-456a-b9a6-264c5bd97c4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_RedeemableNoncontrollingInterestRollForward_1a7dbe8d-98bb-4632-ad47-0cc32c1e9e0b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToNoncontrollingInterest_742c1f25-8f3f-456a-b9a6-264c5bd97c4b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_89eb746e-2ee7-42b9-a52e-0907ec1f0253" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:type="arc" order="41"/>
  </link:definitionLink>
</link:linkbase>
