EXHIBIT 24

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that each person whose
signature appears below hereby constitutes and appoints John A. Roush and Glenn E. Davis, and each of them, his true and lawful attorneys-in-fact and agents, with full power of substitution and re-substitution, for him and in his name, place and
stead, in any and all capacities, to sign the Annual Report on Form 10-K of GSI Group Inc. with respect to the fiscal year ended December 31, 2010 and any and all amendments thereto, and to file the same, together with all exhibits thereto and
all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them and his and their substitute or substitutes, full power and authority to do and perform each
and every act and thing requisite and necessary to be done in connection therewith, as fully for all intents and purposes as he might or could do in person, hereby approving, ratifying and confirming all that such agents and attorneys-in-fact, any
of them or any of his or their substitute or substitutes may lawfully do or cause to be done by virtue hereof.



|                                          |  |                                                              |  |               
|----------------------------------------- |  | ------------------------------------------------------------ |  | --------------
|Signature                                 |  | Title                                                        |  | Date          
|                                          |  |                                                             
|/s/ John A. Roush John A. Roush           |  | Director, Chief Executive Officer                            |  | March 30, 2011
|                                          |  |                                                             
|/s/ Glenn E. Davis Glenn E. Davis         |  | Principal Financial Officer and Principal Accounting Officer |  | March 30, 2011
|                                          |  |                                                             
|/s/ Stephen W. Bershad
Stephen W. Bershad |  | Chairman of the Board of Directors                           |  | March 22, 2011
|                                          |  |                                                             
|/s/ Eugene I. Davis
Eugene I. Davis       |  | Director                                                     |  | March 30, 2011
|                                          |  |                                                             
|/s/ Dennis J. Fortino
Dennis J. Fortino   |  | Director                                                     |  | March 28, 2011
|                                          |  |                                                             
|/s/ K. Peter Heiland
K. Peter Heiland     |  | Director                                                     |  | March 30, 2011
|                                          |  |                                                             
|/s/ Ira J. Lamel Ira J. Lamel             |  | Director                                                     |  | March 30, 2011
|                                          |  |                                                             
|/s/ Byron O. Pond Byron O. Pond           |  | Director                                                     |  | March 22, 2011