The exact number isn't known at the moment but it's apparently a small portion of their staff. http://venturebeat.com/2013/10/01/sega-of-america-lays-off-staff-in-the-u-s/
“As the gaming industry continues to evolve, companies must adapt and adjust in order to compete and succeed in an ever-changing environment. As a result of this, Sega of America has recently undergone a restructure that will enable the company to focus efficiently on developing new and existing content across digital platforms as well as continuing to focus on key brands for packaged goods.”