Patent ID: 8519441

Claim:
A nitride semiconductor device comprising: a substrate being capable of epitaxially growing a nitride semiconductor layer thereon; a semiconductor lamination layer formed on said substrate, and including a channel layer of nitride semiconductor and a cap layer formed above the channel layer; a source area and a drain area defined by partially removing associated portions of the cap layer, the source area and a drain area including separated areas of the channel layer; a source electrode and a drain electrode formed on the source area and the drain area in ohmic contact with said channel layer; an insulating layer being located above and covering the source electrode, the drain electrode, and the cap layer between the source area and the drain area, the insulating layer including an opening formed in a gate electrode contact area, the opening exposing the cap layer at a bottom of the opening, the insulating layer having an outer thickness above the cap layer in remote areas that are spaced apart from the opening, the insulating layer having a side wall defining said opening, where a thickness of the insulating layer over the cap layer increases steeply to an intermediate thickness that is less than the outer thickness, the insulating layer gradually changing thickness in a transient portion that is located between the side wall and the remote areas, the transient portion having a distinctly different slope from that of the side wall, and forming boundaries at the interconnection with the side wall; and a T-shaped gate electrode filling the opening and contacting the cap layer exposed at the bottom of said opening defined by the side wall, the T-shaped gate electrode extending laterally onto portions of the insulating layer.