Patent ID: 7859014

Claim:
A semiconductor device characterized in that: the semiconductor device is a field-effect transistor made of a III-V nitride semiconductor that comprises an insulation film between a gate electrode and a III-V nitride semiconductor layer; the field-effect transistor has a recess structure that is formed by eliminating a part of the III-V nitride semiconductor layer; and the gate electrode and the insulation film are placed in a part or all of the recess area, wherein the insulation film comprises at least a gate insulation film, wherein the gate electrode is formed only on the gate insulation film, wherein a thickness of the insulation film placed between the gate electrode and the semiconductor layer comprises at least a thickness of the gate insulation film, wherein the insulation film placed on the area other than the recess area comprises at least one of a first insulation film and a second insulation film as well as the gate insulation film; wherein the gate insulation film placed on the area other than the recess area is formed on the first insulation film or the second insulation film placed on the area other than the recess area, wherein the first insulation film or the second insulation film placed on the area other than the recess area, on which the gate insulation film placed on the area other than the recess area is formed, is underlying below the gate insulation film, wherein the gate insulation film placed on the area other than the recess area is out of contact with the III-V nitride semiconductor layer, and wherein a material used for the first insulation film or the second insulation film is an insulating substance consisting of one or more of Si, Mg, Hf, Al, Ti and Ta and one or more of O and N.