<SEC-DOCUMENT>0001280452-19-000016.txt : 20190212
<SEC-HEADER>0001280452-19-000016.hdr.sgml : 20190212
<ACCEPTANCE-DATETIME>20190212175954
ACCESSION NUMBER:		0001280452-19-000016
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20190211
FILED AS OF DATE:		20190212
DATE AS OF CHANGE:		20190212

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CHANG KUO WEI HERBERT
		CENTRAL INDEX KEY:			0001192171

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-51026
		FILM NUMBER:		19592413

	MAIL ADDRESS:	
		STREET 1:		C/O MARVELL SEMICONDUCTOR, INC.
		STREET 2:		5488 MARVELL LANE
		CITY:			SANTA CLARA
		STATE:			CA
		ZIP:			95054

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MONOLITHIC POWER SYSTEMS INC
		CENTRAL INDEX KEY:			0001280452
		STANDARD INDUSTRIAL CLASSIFICATION:	SEMICONDUCTORS & RELATED DEVICES [3674]
		IRS NUMBER:				770466789
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		4040 LAKE WASHINGTON BLVD. NE
		STREET 2:		SUITE 201
		CITY:			KIRKLAND
		STATE:			WA
		ZIP:			98033
		BUSINESS PHONE:		425-296-9956

	MAIL ADDRESS:	
		STREET 1:		4040 LAKE WASHINGTON BLVD. NE
		STREET 2:		SUITE 201
		CITY:			KIRKLAND
		STATE:			WA
		ZIP:			98033
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgardoc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-02-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001280452</issuerCik>
        <issuerName>MONOLITHIC POWER SYSTEMS INC</issuerName>
        <issuerTradingSymbol>MPWR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001192171</rptOwnerCik>
            <rptOwnerName>CHANG KUO WEI HERBERT</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4040 LAKE WASHINGTON BLVD. NE, SUITE 201</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>KIRKLAND</rptOwnerCity>
            <rptOwnerState>WA</rptOwnerState>
            <rptOwnerZipCode>98033</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>2019-02-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1339</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12702</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">According to the Company's 2014 Equity Incentive Plan and the Board Compensation Schedule as adopted by the Board on February 11, 2019, each Outside Director will be automatically granted Restricted Stock Units as of such date, if he or she will have served on the Board for at least the preceding six (6) months, with such grant to be effective as of the date of the meeting of the Board or Compensation Committee, as applicable, subject to the Outside Director's continued service to the Board through such date. 100% of the restricted stock units shall vest on the first anniversary of the Vesting Commencement Date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>By: Saria Tseng For: Herbert Chang</signatureName>
        <signatureDate>2019-02-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
