-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 Wz+oppS4cKG28U+r/SxeFTS95pc92/lciYv2W+uGbt8lMf08HAlHOFSUsRGzO5cc
 UmA6V0w+AXjhUDttKWGYfQ==

<SEC-DOCUMENT>0001418215-07-000004.txt : 20071211
<SEC-HEADER>0001418215-07-000004.hdr.sgml : 20071211
<ACCEPTANCE-DATETIME>20071211100729
ACCESSION NUMBER:		0001418215-07-000004
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20071207
FILED AS OF DATE:		20071211
DATE AS OF CHANGE:		20071211

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CASH HARVEY B
		CENTRAL INDEX KEY:			0001198704

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-29823
		FILM NUMBER:		071297575

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		9723927279

	MAIL ADDRESS:	
		STREET 1:		13455 NOEL ROAD
		STREET 2:		SUITE 1670
		CITY:			DALLAS
		STATE:			TX
		ZIP:			75240

	FORMER NAME:	
		FORMER CONFORMED NAME:	CASH H BERRY
		DATE OF NAME CHANGE:	20021015

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SILICON LABORATORIES INC
		CENTRAL INDEX KEY:			0001038074
		STANDARD INDUSTRIAL CLASSIFICATION:	SEMICONDUCTORS & RELATED DEVICES [3674]
		IRS NUMBER:				742793174
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		400 W CESAR CHAVEZ
		CITY:			AUSTIN
		STATE:			TX
		ZIP:			78701
		BUSINESS PHONE:		5124168500

	MAIL ADDRESS:	
		STREET 1:		400 W CESAR CHAVEZ
		CITY:			AUSTIN
		STATE:			TX
		ZIP:			78701
</SEC-HEADER>
<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>2007-12-07</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001198704</rptOwnerCik>
            <rptOwnerName>CASH HARVEY B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>400 WEST CESAR CHAVEZ</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>AUSTIN</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>78701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Non-Qualified Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>38.2</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-12-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2007-12-07</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-12-07</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, $0.0001 par value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The option is immediately exercisable but the shares vest upon the optionee's completion of one year of board service measured from the grant date.</footnote>
        <footnote id="F2">Not applicable per instruction 4(c)(iii).</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Bruce A. Maurer for Harvey B. Cash</signatureName>
        <signatureDate>2007-12-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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