Patent ID: 8450782

Claim:
A field effect transistor made of a nitride compound semiconductor, the field effect transistor comprising: a substrate; a high resistance layer that has a carbon concentration of more than 1×10 18 cm −3 and is formed on the substrate; a semiconductor operation layer that is formed on the high resistance layer and includes a channel layer that has a carbon concentration of not more than 1×10 18 cm −3 and a layer thickness of more than 10 nm and not more than 100 nm; a recess that is formed up to an inside of the channel layer in the semiconductor operation layer; a source electrode and a drain electrode that are formed on the semiconductor operation layer with the recess intervening therebetween; a gate insulating film that is formed on the semiconductor operation layer so as to cover the recess; and a gate electrode formed on the gate insulating film in the recess.