<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0205</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2012-03-26</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001274494</issuerCik>
        <issuerName>FIRST SOLAR, INC.</issuerName>
        <issuerTradingSymbol>FSLR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001545456</rptOwnerCik>
            <rptOwnerName>JCL FSLR Holdings, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>P.O. BOX 1860</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BENTONVILLE</rptOwnerCity>
            <rptOwnerState>AR</rptOwnerState>
            <rptOwnerZipCode>72712</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24957907</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">These shares are owned directly by JCL FSLR Holdings, LLC (&quot;LLC&quot;), which is an entity owned by the John T. Walton Residuary Trust and JCL Holdings, LLC.  On March 26, 2012, Estate of John T. Walton and JCL Holdings, LLC, as members of LLC, transferred the reported shares to LLC.  Thereafter on March 26, 2012, Estate of John T. Walton, a decedent's estate, transferred its entire interest in LLC to John T. Walton Residuary Trust by will and the laws of descent and distribution.  John T. Walton Residuary Trust and JCL Holdings, LLC are the indirect beneficial owners of the reported securities.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Jim Walton, authorized signatory</signatureName>
        <signatureDate>2012-03-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
