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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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<SEC-DOCUMENT>0001212150-05-000001.txt : 20050922
<SEC-HEADER>0001212150-05-000001.hdr.sgml : 20050922
<ACCEPTANCE-DATETIME>20050922162905
ACCESSION NUMBER:		0001212150-05-000001
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050916
FILED AS OF DATE:		20050922
DATE AS OF CHANGE:		20050922

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KRUPKA MICHAEL A
		CENTRAL INDEX KEY:			0001212150

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-19299
		FILM NUMBER:		051098433

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		6175162616

	MAIL ADDRESS:	
		STREET 1:		BAIN CAPITAL
		STREET 2:		111 HUNTINGTON AVE
		CITY:			BOSTON
		STATE:			MA
		ZIP:			021997615

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			INTEGRATED CIRCUIT SYSTEMS INC
		CENTRAL INDEX KEY:			0000874689
		STANDARD INDUSTRIAL CLASSIFICATION:	SEMICONDUCTORS & RELATED DEVICES [3674]
		IRS NUMBER:				232000174
		STATE OF INCORPORATION:			PA
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		2435 BLVD OF THE GENERALS
		CITY:			NORRISTOWN
		STATE:			PA
		ZIP:			19403
		BUSINESS PHONE:		6106305300

	MAIL ADDRESS:	
		STREET 1:		2435 BLVD OF THE GENERALS
		CITY:			NORRISTOWN
		STATE:			PA
		ZIP:			19403
</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>2005-09-16</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000874689</issuerCik>
        <issuerName>INTEGRATED CIRCUIT SYSTEMS INC</issuerName>
        <issuerTradingSymbol>ICST</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001212150</rptOwnerCik>
            <rptOwnerName>KRUPKA MICHAEL A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>BAIN CAPITAL</rptOwnerStreet1>
            <rptOwnerStreet2>111 HUNTINGTON AVE</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>021997615</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Former Director</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2005-09-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>215</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Right to Buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>32.86</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-09-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>16000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2005-08-29</value>
            </exerciseDate>
            <expirationDate>
                <value>2013-08-29</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>16000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Disposed of pursuant to the merger agreemente (&quot;Agreement&quot;) between issuer, Integrated Device Technology, Inc. (&quot;IDT&quot;) and Colonial Merger Sub I, Inc. in exchange for approximately 279 shares of IDT common stock having a market value of $11.23/share on the effective date of the merger, plus approximately $1559.</footnote>
        <footnote id="F2">The option, whether or not exercisable, was cancelled in the merger in exchange for a cash payment of $0 representing the difference between the exercise price of the option and the &quot;Total Purchase Price Per Share&quot; as defined in the Agreement, which on the effective date of the merger was $21.62/share.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Leslie Fleischer</signatureName>
        <signatureDate>2005-09-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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