Monolithic integration of GaN-based semiconductor with Si MEMS is demonstrated from a GaN/Si wafer, in which GaN crystal is grown by molecular beam epitaxy (MBE). A Light emitting diode is fabricated on the grown GaN crystal and the blue electro-luminescence is obtained. The GaN crystal property of is improved by using a template grown by metal organic chemical vapor deposition (MOCVD). A light distribution variable device with Si comb actuator is monolithically fabricated.