UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934
                          (Amendment No.____________)*



                         Monolithic Power Systems, Inc.
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                                (Name of Issuer)


                         Common Stock, $0.001 Par Value
--------------------------------------------------------------------------------
                         (Title of Class of Securities)


                                    609839105

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                                 (CUSIP Number)


                                December 31, 2005
--------------------------------------------------------------------------------
             (Date of Event Which Requires Filing of this Statement)


     Check the appropriate box to designate the rule pursuant to which this
Schedule is filed:

          [_] Rule 13d-1(b)

          [x] Rule 13d-1(c)

          [_] Rule 13d-1(d)

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*    The remainder of this cover page shall be filled out for a reporting
     person's initial filing on this form with respect to the subject class of
     securities, and for any subsequent amendment containing information which
     would alter the disclosures provided in a prior cover page.

     The information required in the remainder of this cover page shall not be
deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise subject to the liabilities of that section of
the Act but shall be subject to all other provisions of the Act (however, see
the Notes).

<PAGE>
CUSIP No. 609839105
            ---------------------

1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

     Philippe Laffont

2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) 
                                                                        (a) [_]
                                                                        (b) [X]

3.   SEC USE ONLY


4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     U.S.A.

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH

5.   SOLE VOTING POWER

     1,921,380

6.   SHARED VOTING POWER

     0

7.   SOLE DISPOSITIVE POWER

     1,921,380

8.   SHARED DISPOSITIVE POWER

     0

9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     1,921,380

10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE
     INSTRUCTIONS)

                                                                            [_]

11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

     6.81%

12.  TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

     IN
--------------------------------------------------------------------------------

<PAGE>
CUSIP No. 609839105
          ---------------------

Item 1(a).  Name of Issuer:

            Monolithic Power Systems, Inc.
            --------------------------------------------------------------------

      (b).  Address of Issuer's Principal Executive Offices:

            983 University Avenue
            Building A
            Los Gatos, CA 95032
            --------------------------------------------------------------------

Item 2(a).  Name, Principal Business Address, and Citizenship of Persons Filing:

            Philippe Laffont - U.S.A.
            126 East 56th Street
            New York, New York 10022
            --------------------------------------------------------------------

      (d).  Title of Class of Securities:

            Common Stock, $0.001 Par Value
            --------------------------------------------------------------------

      (e).  CUSIP Number: 

            609839105
            --------------------------------------------------------------------

Item 3.  If This Statement is filed pursuant to ss.240.13d-1(b) or 240.13d-2(b),
         or (c), check whether the person filing is a:

     (a)  [_] Broker or dealer registered under Section 15 of the Exchange Act
              (15 U.S.C. 78c).

     (b)  [_] Bank as defined in Section 3(a)(6) of the Exchange Act (15 U.S.C.
              78c).

     (c)  [_] Insurance company as defined in Section 3(a)(19) of the Exchange
              Act (15 U.S.C. 78c).

     (d)  [_] Investment company registered under Section 8 of the Investment
              Company Act of 1940 (15 U.S.C. 80a-8).

     (e)  [_] An investment adviser in accordance with s.240.13d-1(b)(1)(ii)(E);

     (f)  [_] An employee benefit plan or endowment fund in accordance with
              s.240.13d-1(b)(1)(ii)(F);

     (g)  [_] A parent holding company or control person in accordance with Rule
              13d-1(b)(1)(ii)(G);

     (h)  [_] A savings association as defined in Section 3(b) of the Federal
              Deposit Insurance Act (12 U.S.C.1813);

     (i)  [_] A church plan that is excluded from the definition of an
              investment company under Section 3(c)(14) of the Investment
              Company Act of 1940 (15 U.S.C. 80a-3);

     (j)  [_] Group, in accordance with s.240.13d-1(b)(1)(ii)(J).

Item 4.  Ownership.

     Provide the following information regarding the aggregate number and
percentage of the class of securities of the issuer identified in Item 1.

     (a) Amount beneficially owned:

         Philippe Laffont - 1,921,380
         -----------------------------------------------------------------------

     (b) Percent of class:

         Philippe Laffont - 6.81%
         -----------------------------------------------------------------------

     (c) Number of shares as to which the person has:

          (i)  Sole power to vote or to direct the vote:

               Philippe Laffont - 1,921,380 

          (ii) Shared power to vote or to direct the vote:

               Philippe Laffont - 0

         (iii) Sole power to dispose or to direct the disposition of:

               Philippe Laffont - 1,921,380

          (iv) Shared power to dispose or to direct the disposition of:

               Philippe Laffont - 0

Item 5.  Ownership of Five Percent or Less of a Class.

     If this statement is being filed to report the fact that as of the date
hereof the reporting person has ceased to be the beneficial owner of more than
five percent of the class of securities, check the following [_].

         N/A
         -----------------------------------------------------------------------

Item 6.  Ownership of More Than Five Percent on Behalf of Another Person.

         If any other person is known to have the right to receive or the power
to direct the receipt of dividends from, or the proceeds from the sale of, such
securities, a statement to that effect should be included in response to this
item and, if such interest relates to more than five percent of the class, such
person should be identified. A listing of the shareholders of an investment
company registered under the Investment Company Act of 1940 or the beneficiaries
of employee benefit plan, pension fund or endowment fund is not required.

         The securities are held in the name of two private investment funds.
Philippe Laffont is reporting beneficial ownership under Item 4 as the managing
member of the investment manager and general partner of these funds.

         Mr. Laffont disclaims beneficial ownership in the shares reported
herein except to the extent of his pecuniary interest therein.
         -----------------------------------------------------------------------

Item 7.  Identification and Classification of the Subsidiary Which Acquired
         the Security Being Reported on by the Parent Holding Company or Control
         Person.

         If a parent holding company or Control person has filed this schedule,
pursuant to Rule 13d-1(b)(1)(ii)(G), so indicate under Item 3(g) and attach an
exhibit stating the identity and the Item 3 classification of the relevant
subsidiary. If a parent holding company or control person has filed this
schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating
the identification of the relevant subsidiary.

         N/A
         -----------------------------------------------------------------------

Item 8.  Identification  and  Classification  of Members of the Group.

         If a group has filed this schedule pursuant to
ss.240.13d-1(b)(1)(ii)(J), so indicate under Item 3(j) and attach an exhibit
stating the identity and Item 3 classification of each member of the group. If a
group has filed this schedule pursuant to ss.240.13d-1(c) or ss.240.13d-1(d),
attach an exhibit stating the identity of each member of the group.

         N/A
         -----------------------------------------------------------------------

Item 9.  Notice of Dissolution of Group.

         Notice of dissolution of a group may be furnished as an exhibit stating
the date of the dissolution and that all further filings with respect to
transactions in the security reported on will be filed, if required, by members
of the group, in their individual capacity. See Item 5.

         N/A
         -----------------------------------------------------------------------

Item 10. Certification.

     (b) The following certification shall be included if the statement is
         filed pursuant to Rule 13d-1(c):

         By signing below I certify that, to the best of my knowledge and
         belief, the securities referred to above were not acquired and are not
         held for the purpose of or with the effect of changing or influencing
         the control of the issuer of the securities and were not acquired and
         are not held in connection with or as a participant in any transaction
         having such purpose or effect.

     After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

Philippe Laffont*


/s/ Philippe Laffont
------------------------

February 14, 2006

*The Reporting Person disclaims beneficial ownership in the shares reported
herein except to the extent of his pecuniary interest therein.

SK 02984 0001 641369