Abstract: A semiconductor device formed from a III-V nitride family semiconductor is disclosed that has a reduced gate leakage current and good interface characteristics between the III-V nitride family semiconductor and a gate insulating film. The semiconductor device includes a semiconductor layer formed from the III-V nitride family semiconductor, a gate insulating film on the semiconductor layer, and a gate electrode on the gate insulating film. The gate insulating film is formed from one of a tantalum oxide, a hafnium oxide, a hafnium aluminum oxide, a lanthanum oxide, and a yttrium oxide.

Abstract: A method for manufacturing a semiconductor device includes a step of forming a layer where a gate electrode aperture is to be formed including at least one ultraviolet resist layer on the surface where a gate electrode is to be formed, and forming a gate electrode aperture in the layer where a gate electrode aperture is to be formed; a step of forming a layer where an over-gate is to be formed in which an over-gate part of a gate electrode is to be formed, on the layer where a gate electrode aperture is to be formed; a step of reducing the width of the gate electrode aperture; and a step of forming the gate electrode in the gate electrode aperture. The method makes it possible to efficiently produce a fine gate electrode by thickening the gate electrode aperture and reducing the width of the gate electrode aperture.