FORM 4
[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      

1. Name and Address of Reporting Person *

Xiao Deming 		2. Issuer Name and Ticker or Trading Symbol

MONOLITHIC POWER SYSTEMS INC [ MPWR ] 		5. Relationship of Reporting Person(s) to Issuer (Check all applicable)

_____ Director                      _____ 10% Owner
__ X __ Officer (give title below)      _____ Other (specify below)
Pres. of MPS Asia Operations
(Last)          (First)          (Middle)

79 GREAT OAKS BLVD 		3. Date of Earliest Transaction (MM/DD/YYYY)

2/3/2015
(Street)

SAN JOSE, CA 95119
(City)        (State)        (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)

 
6. Individual or Joint/Group Filing (Check Applicable Line)

_ X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3) 		2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. Code
(Instr. 8) 		4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5) 		5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4) 		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V Amount (A) or (D) Price
Common Stock   2/3/2015   (1)   M (1)    43200.0   (1) A $0.0   285512   D    
Common Stock   2/17/2015     J (2)    474.0   A $37.451   258375   D    
Common Stock   2/3/2015     A    569.0   (3) A $0.0   2148   I   by Spouse  
Common Stock   3/16/2015     S (4)    9.0   D $53.16   2139   I   by Spouse  
Common Stock   3/16/2015     S (4)    166.0   D $53.16   1973   I   by Spouse  
Common Stock   3/16/2015     S (4)    84.0   D $53.16   1889   I   by Spouse  

Table II - Derivative Securities Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3) 		2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. Code
(Instr. 8) 		5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5) 		6. Date Exercisable and Expiration Date 7. Title and Amount of Securities Underlying Derivative Security
(Instr. 3 and 4) 		8. Price of Derivative Security
(Instr. 5) 		9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Performance Shares     (5) 2/3/2015   (1)   M   (1)       43200.0   (1)     (5)   (5) Common Stock   43200   $0.0   86400   D    

Explanation of Responses:
( 1)  Each performance share represents a contingent right to receive a restricted stock unit upon MPWR's common stock achieving a 20-day average closing price of $47.00 per share from January 1, 2014 through December 31, 2018 (the "Performance Period"). Credited performance units are still subject to an additional, quarterly, five-year time-based vesting schedule beginning January 1, 2019, subject to acceleration under certain circumstances.
( 2)  Acquired through the Company's qualified ESPP program.
( 3)  1/16 of the Restricted Stock Units shall vest quarterly following the Vesting Commencement Date, provided that the Grantee continues to be a Service Provider from the Grant Date through each applicable vesting date.
( 4)  Shares sold to pay tax obligations resulting from the vesting of restricted stock units.
( 5)  Each performance unit will vest as follows: one share of MPWR common stock will be credited for each performance unit if the price of MPWR common stock achieves a 20-day average closing price of $40.00 per share from January 1, 2014 through December 31, 2018 (the "Performance Period"), and up to four additional shares will be credited for each performance unit if the 20-day average closing price reaches $43.00, $47.00, $52.00 and $56.00 (that is, one share per price level) during the Performance Period. Credited performance units are then subject to an additional, quarterly, five-year time-based vesting schedule beginning January 1, 2019, subject to acceleration under certain circumstances.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
Xiao Deming
79 GREAT OAKS BLVD
SAN JOSE, CA 95119

Pres. of MPS Asia Operations

Signatures
By: Saria Tseng For: Deming Xiao 3/18/2015
** Signature of Reporting Person Date


Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.
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