The performance of double gate GaSb nMOSFETs with surface orientations of (100) and (111) are compared by deterministically solving the time-dependent Boltzmann transport equation (BTE).Results show that the on-state current of the device with (111) surface orientation is almost three times larger than the (100) case due to the higher injection velocity.Moreover,the scattering rate of the (111) device is slightly lower than that of the (100) device.