-----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,
 JTfInp4tWb8FG0cX5w+CcnmNCD94WxdpulcsiOaEjkk6yH9YIgcnq6NrvBi3LVh4
 9EA2hXuDNpdIyVF/lnhK7A==

<SEC-DOCUMENT>0001195890-03-000002.txt : 20031017
<SEC-HEADER>0001195890-03-000002.hdr.sgml : 20031017
<ACCEPTANCE-DATETIME>20031017175402
ACCESSION NUMBER:		0001195890-03-000002
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20031016
FILED AS OF DATE:		20031017

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CHOY BENEDICT C K
		CENTRAL INDEX KEY:			0001195890

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-12718
		FILM NUMBER:		03946818

	BUSINESS ADDRESS:	
		STREET 1:		1235 BORDEAUX DRIVE
		CITY:			SUNNYVALE
		STATE:			CA
		ZIP:			94089

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SUPERTEX INC
		CENTRAL INDEX KEY:			0000730000
		STANDARD INDUSTRIAL CLASSIFICATION:	SEMICONDUCTORS & RELATED DEVICES [3674]
		IRS NUMBER:				942328535
		STATE OF INCORPORATION:			CA
		FISCAL YEAR END:			0331

	BUSINESS ADDRESS:	
		STREET 1:		1235 BORDEAUX DR
		CITY:			SUNNYVALE
		STATE:			CA
		ZIP:			94089
		BUSINESS PHONE:		4087440100

	MAIL ADDRESS:	
		STREET 1:		1235 BORDEAUX DR
		CITY:			SUNNYVALE
		STATE:			CA
		ZIP:			94089
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>

<ownershipDocument>

    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2003-10-16</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000730000</issuerCik>
        <issuerName>SUPERTEX INC</issuerName>
        <issuerTradingSymbol>SUPX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001195890</rptOwnerCik>
            <rptOwnerName>CHOY BENEDICT C K</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior Vice President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>

        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2003-10-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>12000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>229304</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>

    </nonDerivativeTable>

    <derivativeTable>

        <derivativeTransaction>
            <securityTitle>
                <value>ISO Option (to purchase Common Stock)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>12</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2003-10-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>12000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2001-03-03</value>
            </exerciseDate>
            <expirationDate>
                <value>2004-03-03</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>10000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>

    </derivativeTable>

    <footnotes>
        <footnote id="F1">Other Grants:  NQ Option (to purchase common stock).  Exercise Price $12.0000.  Shares granted: 4,000.  Shares exercisable currently: 4,000.  Expiration date: 3/3/2004.  Held direct.</footnote>
        <footnote id="F2">Other Grants:  ISO Option (to purchase common stock).  Exercise Price $10.7500.  Shares granted: 45,000.  Shares currently exercisable: 9,000.  9,000 shares exercisable on 6/1/2004.  9,000 shares exercisable on 6/1/2005.  9,000 shares exercisable on 6/1/2006.  9,000 shares exercisable on 6/1/2007.  Expiration date: 6/1/2008.  Held direct.</footnote>
        <footnote id="F3">Other Grants:  NQ Option (to purchase common stock).  Exercisable Price: $10.7500.   Shares exercisable currently: 7,000.   Expiration date: 6/1/2005.  Held direct.</footnote>
        <footnote id="F4">Other Grants:  NQ Option (to puchase common stock).  Exercise price $15.5000.  Shares granted 20,000.  Shares Exercisable currently: 12,000.  4,000 shares exercisable on 12/1/2003.  4,000 shares exercisable on 12/1/2004.  Expiration date: 12/1/2006.  Held Direct.</footnote>
        <footnote id="F5">Other Grants:  NQ option (to purchase common stock).  Exercise price: $12.5300.  Shares granted 20,000.  Shares currently exercisable: 3,000.  3,000 shares exercisable on 6/1/2004.  7,000 shares exercisable on 6/1/2005.  7,000 shares exercisable on 6/1/2006.  Expiration date: 6/1/2008.  Held direct.</footnote>
    </footnotes>


    <ownerSignature>
        <signatureName>Benedict Choy</signatureName>
        <signatureDate>2003-10-17</signatureDate>
    </ownerSignature>

</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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