Abstract: A power device having a patterned three-dimensional gate geometry is fabricated and described. The power device achieved increased effective gate width and increased channel conductivity per unit length. It includes at least a channel layer, a barrier layer, a dielectric layer, a gate disposed on the dielectric layer, dielectric layer disposed on the barrier layer and the channel layer, respectively. Gate includes protruding sections and extending sections directly contacting the dielectric layer. Dielectric layer includes a repeating rectangular-wave structure. The dielectric layer forms a gate oxide directly contacting trenches of channel layer. Alternatively, gate oxide can be disposed directly on a p-doped GaN filled region which includes an alternating repeating rectangular-wave structure.