<SEC-DOCUMENT>0001280452-21-000036.txt : 20210223
<SEC-HEADER>0001280452-21-000036.hdr.sgml : 20210223
<ACCEPTANCE-DATETIME>20210223180809
ACCESSION NUMBER:		0001280452-21-000036
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20210216
FILED AS OF DATE:		20210223
DATE AS OF CHANGE:		20210223

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BLEGEN THEODORE
		CENTRAL INDEX KEY:			0001415033

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-51026
		FILM NUMBER:		21667218

	MAIL ADDRESS:	
		STREET 1:		5808 LAKE WASHINGTON BLVD NE
		CITY:			KIRKLAND
		STATE:			WA
		ZIP:			98033

	FORMER NAME:	
		FORMER CONFORMED NAME:	Blegen Theodore
		DATE OF NAME CHANGE:	20071012

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:		5808 LAKE WASHINGTON BLVD. NE
		CITY:			KIRKLAND
		STATE:			WA
		ZIP:			98033
		BUSINESS PHONE:		425-296-9956

	MAIL ADDRESS:	
		STREET 1:		5808 LAKE WASHINGTON BLVD. NE
		CITY:			KIRKLAND
		STATE:			WA
		ZIP:			98033
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgardoc.xml
<DESCRIPTION>PRIMARY DOCUMENT
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    <periodOfReport>2021-02-16</periodOfReport>

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

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            <rptOwnerCik>0001415033</rptOwnerCik>
            <rptOwnerName>BLEGEN THEODORE</rptOwnerName>
        </reportingOwnerId>
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            <rptOwnerStreet1>5808 LAKE WASHINGTON BLVD NE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>KIRKLAND</rptOwnerCity>
            <rptOwnerState>WA</rptOwnerState>
            <rptOwnerZipCode>98033</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>CFO</officerTitle>
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    </reportingOwner>

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            <transactionDate>
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                <transactionPricePerShare>
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                    <footnoteId id="F4"/>
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                <transactionAcquiredDisposedCode>
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                <sharesOwnedFollowingTransaction>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-02-19</value>
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            <transactionCoding>
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                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
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            <transactionAmounts>
                <transactionShares>
                    <value>208</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>385.0028</value>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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                </directOrIndirectOwnership>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
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            </securityTitle>
            <transactionDate>
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            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
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            <transactionAmounts>
                <transactionShares>
                    <value>400</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>386.1075</value>
                    <footnoteId id="F6"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
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            </securityTitle>
            <transactionDate>
                <value>2021-02-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1031</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>387.2877</value>
                    <footnoteId id="F7"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
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                </directOrIndirectOwnership>
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        <nonDerivativeTransaction>
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            <transactionDate>
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                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
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            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
                    <value>388.3591</value>
                    <footnoteId id="F8"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
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            <securityTitle>
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            <transactionDate>
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            </transactionDate>
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                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
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            <transactionAmounts>
                <transactionShares>
                    <value>250</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>389.106</value>
                    <footnoteId id="F9"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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            <securityTitle>
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            <transactionDate>
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            </transactionDate>
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                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
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                </transactionShares>
                <transactionPricePerShare>
                    <value>390.4108</value>
                    <footnoteId id="F10"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            <transactionDate>
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                <equitySwapInvolved>0</equitySwapInvolved>
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                </transactionShares>
                <transactionPricePerShare>
                    <value>391.355</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
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            <transactionDate>
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                <transactionCode>S</transactionCode>
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                <footnoteId id="F2"/>
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                <transactionPricePerShare>
                    <value>392.495</value>
                    <footnoteId id="F11"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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                </sharesOwnedFollowingTransaction>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
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            </transactionDate>
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                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>92</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>393.44</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>158899</value>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
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        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Acquired through the Company's qualified ESPP program.</footnote>
        <footnote id="F2">In accordance with the reporting person's 10b5-1 trading plan.</footnote>
        <footnote id="F3">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $382.10 to $383.08.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F4">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $383.33 to $384.32.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F5">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $384.51 to $385.17.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F6">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $385.69 to $386.39.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F7">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $386.76 to $387.71.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F8">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $387.84 to $388.80.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F9">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $388.99 to $389.24.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F10">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $390.14 to $390.77.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F11">The price is the weighted average sale price for the transactions reported on this line.  The prices for the transactions reported on this line range from $392.19 to $392.80.  The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>By: Saria Tseng For: Bernie Blegen</signatureName>
        <signatureDate>2021-02-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
