Patent ID: 8890210

Claim:
A field effect transistor, comprising: a nitride semiconductor multilayer structure formed on an upper surface of a substrate and including a heterojunction; a source electrode and a drain electrode formed on the nitride semiconductor multilayer structure; a gate electrode formed between the source electrode and the drain electrode; an insulating film formed on the nitride semiconductor multilayer structure; and a field plate formed on and in contact with an upper surface of the insulating film, and having an end located between the gate electrode and the drain electrode, wherein the insulating film includes a first film and a second film sequentially formed on the nitride semiconductor multilayer structure, an opening exposing the source electrode is formed in the insulating film, and a thin film portion which is formed between the gate electrode and the drain electrode and in which at least part of the second film is removed so as to form a recess in an upper surface of the insulating film, the thin film portion having an upper surface which is closer to the upper surface of the substrate than an upper surface of the second film outside the thin film portion, the insulating film having a thickness in the thin film portion which is less than a thickness of the insulating film outside the thin film portion, the first film covers an upper surface of the gate electrode, the second film is formed on an upper surface of the first film and has a dielectric breakdown voltage lower than that of the first film, and the field plate covers the thin film portion, and is connected to the source electrode in the opening.