<SUBMISSION>
<ACCESSION-NUMBER>0001285081-05-000078
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20050912
<FILING-DATE>20050914
<DATE-OF-FILING-DATE-CHANGE>20050914
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>SILICON LABORATORIES INC
<CIK>0001038074
<ASSIGNED-SIC>3674
<IRS-NUMBER>742793174
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>4635 BOSTON LN
<CITY>AUSTIN
<STATE>TX
<ZIP>78735
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>4635 BOSTON LANE
<CITY>AUSTIN
<STATE>TX
<ZIP>78735
</MAIL-ADDRESS>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>COKER DERRELL C
<CIK>0001066597
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-29823
<FILM-NUMBER>051085320
</FILING-VALUES>
<BUSINESS-ADDRESS>
<PHONE>6034298761
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>UNITRODE CORP
<STREET2>7 CONTINENTAL BLVD
<CITY>MERRIMACK
<STATE>NH
<ZIP>03054
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-09-12</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001038074</issuerCik>
        <issuerName>SILICON LABORATORIES INC</issuerName>
        <issuerTradingSymbol>SLAB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001066597</rptOwnerCik>
            <rptOwnerName>COKER DERRELL C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4635 BOSTON LN</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>AUSTIN</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>78735</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $0.0001 par value</value>
            </securityTitle>
            <transactionDate>
                <value>2005-09-12</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8125</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.0001</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>101562</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Reflects the grant of restricted stock units that will entitle the Reporting
Person to receive one share of common stock per restricted stock unit. The
restricted stock units vest at the rate of 20% per year on each anniversary
date after September 12, 2005 and will be settled pursuant to the terms of the
Issuer's 2000 Stock Incentive Plan.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Derrell C. Coker</signatureName>
        <signatureDate>2005-09-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
