UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G
Under the Securities Exchange Act of 1934
(Amendment No. ___________)*


Mattson Technology Inc.
(Name of Issuer)

 Common
(Title of Class of Securities)

577223100
(CUSIP Number)

December 31, 2010
(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to
which this Schedule is filed:
[X ]	Rule 13d-1(b)
[  ]	Rule 13d-1(c)
[  ]	Rule 13d-1(d)

*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).

CUSIP No.  577223100





1.	Names of Reporting Persons.
I.R.S. Identification Nos. of above persons (entities
only).
     Donald Smith & Co., Inc.
	        13-2807845

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
		A Delaware Corporation

Number of           5.	Sole Voting Power    0 shares
Shares
Beneficially		6.	Shared Voting Power       0
Owned by
Each Reporting		7.	Sole Dispositive Power 2,796,043 shares
Person With
				8.	Shared Dispositive Power   0


9.Aggregate Amount Beneficially Owned by Each Reporting Person
                  2,796,043 shares


10.	Check if the Aggregate Amount in Row (9) Excludes Certain
Shares (See Instructions)

11.	Percent of Class Represented by Amount in Row (9) 5.43%
12.	Type of Reporting Person (See Instructions)       IA




1.	Names of Reporting Persons.
I.R.S. Identification Nos. of above persons (entities
only).
     Donald Smith Value Fund, L.P.
	        27-0229715

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
		A Delaware Corporation

Number of           5.	Sole Voting Power    2,731,043 shares
Shares
Beneficially		6.	Shared Voting Power       0
Owned by
Each Reporting		7.	Sole Dispositive Power 2,796,043 shares
Person With
				8.	Shared Dispositive Power   0


9.Aggregate Amount Beneficially Owned by Each Reporting Person
                  2,796,043 shares


10.	Check if the Aggregate Amount in Row (9) Excludes Certain
Shares (See Instructions)

11.	Percent of Class Represented by Amount in Row (9) 5.43%
12.	Type of Reporting Person (See Instructions)       PN




1.	Names of Reporting Persons.
I.R.S. Identification Nos. of above persons (entities
only).
     Donald Smith


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
		A Delaware Corporation

Number of           5.	Sole Voting Power    65,000 shares
Shares
Beneficially		6.	Shared Voting Power       0
Owned by
Each Reporting		7.	Sole Dispositive Power 2,796,043 shares
Person With
				8.	Shared Dispositive Power   0


9.Aggregate Amount Beneficially Owned by Each Reporting Person
                  2,796,043 shares


10.	Check if the Aggregate Amount in Row (9) Excludes Certain
Shares (See Instructions)

11.	Percent of Class Represented by Amount in Row (9) 5.43%
12.	Type of Reporting Person (See Instructions)       IN




Item 1.

(a)	Name of Issuer: Mattson Technology Inc.
(b)	Address of Issuer's Principal Executive Offices
			47131 Bayside Parkway
			Fremont, CA  94538
Item 2.

	(a)	Name of Person Filing: Donald Smith & Co.,Inc.

	(b)	Address of Principal Business Office:
		152 West 57th Street
		New York, NY 10019

	(c)	Citizenship:    A Delaware Corporation

	(d)	Title of Class of Securities: Common

      (e)	CUSIP Number: 577223100




Item 3.	This statement is filed pursuant to Section 240.13d-1(b),
and the person filing is an investment advisor registered
in accordance with Section 240.13d-1(b)(1)(ii)(E);

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:   	2,796,043

	(b)	Percent of class:   		5.43%

	(c)	Number of shares as to which the person has:
	(i)	SOLE POWER TO VOTE: 		2,796,043
	(ii)	SHARED POWER TO VOTE:		SEE ITEM 6 OF COVER PAGE
	(iii)	SOLE POWER TO DISPOSE:	2,796,043
	(iv)	SHARED POWER TO DISPOSE:	SEE ITEM 8 OF COVER PAGE

Item 5.	Ownership of Five Percent or Less is NOT APPLICABLE

Item 6.	Ownership of More than Five Percent on Behalf of Another Person:
1. Donald Smith & Co., Inc. does not serve as custodian of
the assets of any of its clients; accordingly, in each
instance only the client or the client?s custodian or
trustee bank has the right to receive dividends paid
with respect to, and proceeds from the sale of, such
securities.


Item 7.	Identification and Classification of the Subsidiary Which Acquired
the Security Being Reported on By the Parent Holding Company
 		NOT APPLICABLE

Item 8.	Identification and Classification of Members of the Group
 		See EXHIBIT A

Item 9.	Notice of Dissolution of Group
	NOT APPLICABLE

Item 10.	Certification

	(a)
By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were acquired and are held
in the ordinary course of business and 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 that purpose or effect.


SIGNATURE
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.

March 29, 2011
Date

Donald G. Smith___________
Signature

President_________________
Title



SCHEDULE 13G - TO BE INCLUDED IN
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
	RULE 13d-1(f)(1)  EXHIBIT A:

Donald Smith & Co., Inc.	IA
Donald Smith Value Fund, L.P.   PN
Donald Smith, IN





SCHEDULE 13G - TO BE INCLUDED IN
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
	RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on March 29, 2011,
agree and consent to the joint filing on their behalf of this
Schedule 13G in connection with their beneficial ownership
of the Common Stock of Mattson Technology Inc. at
December 31, 2010.

	Donald Smith & Co., Inc.

	By /s/ Donald G. Smith
	Donald G.Smith
	President
	Duly authorized by and on behalf of Donald Smith & Co., Inc.


	Donald Smith Value Fund, L.P.

	By /s/ Donald G. Smith
	Donald G.Smith
	President
	Duly authorized by and on behalf of
		Donald Smith Value Fund, L.P


	Donald G. Smith

	By /s/ Donald G. Smith
	Donald G.Smith
	President