<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType><periodOfReport>2004-01-08</periodOfReport><notSubjectToSection16>1</notSubjectToSection16>
    <issuer>
        <issuerCik>0001058057</issuerCik>
        <issuerName>MARVELL TECHNOLOGY GROUP LTD</issuerName>
        <issuerTradingSymbol>MRVL</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001134607</rptOwnerCik>
            <rptOwnerName>BANATAO DIOSDADO P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>700 FIRST AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SUNNYVALE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94089</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><nonDerivativeTable><nonDerivativeTransaction><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2004-01-08</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>M</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>25000</value></transactionShares><transactionPricePerShare><value>.05</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1400000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeTransaction><nonDerivativeTransaction><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2004-01-08</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>25000</value></transactionShares><transactionPricePerShare><value>41.8344</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1375000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeTransaction><nonDerivativeHolding><securityTitle><value>Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1676747</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosdado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>680680</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Tallwood Partners LLC</value></natureOfOwnership></ownershipNature></nonDerivativeHolding></nonDerivativeTable><derivativeTable><derivativeTransaction><securityTitle><value>Stock Option (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>.05</value></conversionOrExercisePrice><transactionDate><value>2004-01-08</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>M</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>25000</value></transactionShares><transactionPricePerShare><value>0</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><footnoteId id="F1"/></exerciseDate><expirationDate><value>2007-01-28</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>6100</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>6100</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction><derivativeHolding><securityTitle><value>Stock Option (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>15.00</value></conversionOrExercisePrice><exerciseDate><footnoteId id="F2"/></exerciseDate><expirationDate><value>2010-06-26</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>20500</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>20500</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F3"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F3"/></exerciseDate><expirationDate><value>2004-03-05</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>500000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Tallwood Partners LLC</value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F4"/><footnoteId id="F5"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F4"/><footnoteId id="F5"/></exerciseDate><expirationDate><value>2004-03-05</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>250000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosdado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F4"/><footnoteId id="F5"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F4"/><footnoteId id="F5"/></exerciseDate><expirationDate><value>2004-03-12</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>150000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosdado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F4"/><footnoteId id="F5"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F4"/><footnoteId id="F5"/></exerciseDate><expirationDate><value>2004-03-12</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>100000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosdado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F4"/><footnoteId id="F5"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F4"/><footnoteId id="F5"/></exerciseDate><expirationDate><value>2005-06-28</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>300000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosdado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F4"/><footnoteId id="F5"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F4"/><footnoteId id="F5"/></exerciseDate><expirationDate><value>2005-09-09</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>100000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F4"/><footnoteId id="F5"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F4"/><footnoteId id="F5"/></exerciseDate><expirationDate><value>2005-09-23</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>100000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosdado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F4"/><footnoteId id="F5"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F4"/><footnoteId id="F5"/></exerciseDate><expirationDate><value>2006-06-30</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>280000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosdado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Put  Option (Right to Sell)</value></securityTitle><conversionOrExercisePrice><footnoteId id="F4"/><footnoteId id="F5"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F4"/><footnoteId id="F5"/></exerciseDate><expirationDate><value>2006-10-13</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>150000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Diosdado &amp; Maria C. Banatao Trust</value></natureOfOwnership></ownershipNature></derivativeHolding></derivativeTable><footnotes><footnote id="F1">These shares are fully vested and immediately exerciseable.  Any unexercised shares will be cancelled after 01/09/04.</footnote><footnote id="F2">The Reporting Person previously reported an option to purchase 30,000 shares, of which 20,500 are vested and exerciseable until 01/09/04.  Any unexercised shares will be cancelled after 01/09/04.  </footnote><footnote id="F3">The Reporting Person also has indirect ownership of a pre-paid forward contract (Right to Sell) held by Tallwood Partners LLC (the &quot;Partnership&quot;).  The contract provides that the Partnership deliver a certain number of shares at the end of the contract depending on the Issuer's common stock price on such date. The contract for 500,000 shares was entered into on 11/30/01 with a settlement date on 03/05/04.  Exact pricing terms are determined in accordance with the contract.</footnote><footnote id="F4">The Reporting Person also has indirect ownership of seven prepaid forward contracts (Right to Sell) held by the Diosdado &amp; Maria C. Banatao Trust (the &quot;Trust&quot;). The contracts provide that the Trust will deliver a certain number of shares at the end of the contract depending on the Issuer's common stock price on such date. 1) a contract for 250,000 shares was entered into on  03/07/02 with a settlement date on 03/05/04; 2) a contract for 150,000 shares was entered into on 03/12/02 with a settlement date on 03/12/04; 3) a contract for 100,000 shares was entered into on 04/01/02 with a settlement date on 03/12/04; 4)  a contract for 300,000 shares was entered into on 06/28/02 with a settelement date on 06/28/05; 5) a contract for 100,000 shares was entered into on 09/10/02 with a settlement date on 09/09/05; 6) a contract for 100,000 shares was entered into on 09/23/02 with a settlement date on 09/23/05; 7) a contract for 280,000 shares was entered into on 07/02/03 with a settlement date </footnote><footnote id="F5">Continuation of Footnote No. 7:  on 06/30/06; 8) a contract for 150,000 shares was entered into on 10/14/03 with a settlement date on 10/13/06.   Exact pricing terms for each contract are determined on the respective settlement dates in accordance with the applicable contract.</footnote></footnotes><remarks/><ownerSignature><signatureName>Diosdado Banatao</signatureName><signatureDate>2004-01-12</signatureDate></ownerSignature></ownershipDocument>

