Patent ID: 8072002

Claim:
A field effect transistor formed of a semiconductor of a III group nitride compound, comprising: an electron running layer formed on a substrate and formed of GaN; an electron supplying layer formed on the electron running layer and formed of Al x Ga 1-x N (0.01â‰¦xâ‰¦0.4), said electron supplying layer having a band gap energy different from that of the electron running layer and being divided with a recess region having a depth reaching the electron running layer; a source electrode and a drain electrode formed on the electron supplying layer with the recess region in between; a gate insulating film layer formed on the electron supplying layer for covering a surface of the electron running layer in the recess region; and a gate electrode formed on the gate insulating film layer in the recess region, wherein said electron running layer comprises a lower part layer and an upper part layer formed on the lower part layer and having a density of an acceptor different from that of the lower part layer, said recess region having the depth reaching to the lower part layer.