Patent ID: 8093626

Claim:
A field effect transistor comprising: a substrate; a semiconductor layer of a first conductivity-type III-nitride semiconductor formed on the substrate, the semiconductor layer including a channel region; a gate insulating film formed on the channel region; a gate electrode formed on the gate insulating film; source and drain contact regions of a second conductivity type formed on respective sides of the channel region; source and drain electrodes formed in ohmic contact with the source and drain contact regions, respectively; and a RESURF region formed in the channel region and adjacent to the drain contact region, the RESURF region having a sheet carrier concentration ranging from 1×10 12 cm −2 to 5×10 13 cm −2 , wherein the semiconductor layer is a p-type GaN layer, the RESURF region is an n-type GaN layer formed by ion-implanting an n-type impurity into the p-type GaN layer, and the p-type GaN layer of the semiconductor layer has a p-type impurity concentration ranging from 1×10 15 cm −3 to 5×10 17 cm −3 .