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

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-02-20</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001333822</issuerCik>
        <issuerName>SemiLEDs Corp</issuerName>
        <issuerTradingSymbol>LEDS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001506244</rptOwnerCik>
            <rptOwnerName>Young David</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3F, NO. 11 KE JUNG RD., CHU-NAN SITE</rptOwnerStreet1>
            <rptOwnerStreet2>HSINCHU SCIENCE PARK, MIAO-LI COUNTY</rptOwnerStreet2>
            <rptOwnerCity>CHU-NAN</rptOwnerCity>
            <rptOwnerState>F5</rptOwnerState>
            <rptOwnerZipCode>350</rptOwnerZipCode>
            <rptOwnerStateDescription>TAIWAN, PROVINCE OF CHINA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>CFO and Treasurer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-02-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>50000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>103571</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">These shares represent restricted stock units and will be settled in LEDS common stock upon vesting. 25% of the restricted stock units will vest on February 20 in each of 2013, 2014, 2015 and 2016 and will become fully vested upon a change in control. Vested shares will be delivered to the reporting person within the first open trading window following the vesting date, but in no event later than the 15th day of the 3rd month following the end of the Company's tax year that includes the vesting date.</footnote>
    </footnotes>

    <remarks>Exhibit List Exhibit 24.1: Power of Attorney</remarks>

    <ownerSignature>
        <signatureName>/s/ Yingku (Adam) Lin, attorney-in-fact</signatureName>
        <signatureDate>2012-02-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
