Enhancement-mode GaN devices having a gate spacer, a gate metal material and a gate compound that are self-aligned, and a methods of forming the same. The materials are patterned and etched using a single photo mask, which reduces manufacturing costs. An interface of the gate spacer and the gate compound has lower leakage than the interface of a dielectric film and the gate compound, thereby reducing gate leakage. In addition, an ohmic contact metal layer is used as a field plate to relieve the electric field at a doped III-V gate compound corner towards the drain contact, which leads to lower gate leakage current and improved gate reliability.