Abstract: GaN vertical trench MOSFETs and methods of manufacturing the same are disclosed. One example embodiment is a vertical trench MOSFET. The MOSFET includes a semiconductor transistor that has a first surface and a second surface, and a trench that extends from the first surface into the semiconductor transistor along a first direction perpendicular to the first and second surfaces. The semiconductor transistor includes a body region having a channel region arranged along the first direction along at least a portion of a wall of the trench. The doping concentration of the channel region is non-uniform. As a non-limiting example, two-step doping is conducted for forming asymmetric or non-uniform channel of a GaN vertical trench MOSFET. In some embodiments, multiple-step doping other than the two-step doing (such as doping in three steps, four steps, or more), linearly scaled doping, other proper asymmetric doping can be used.