Patent ID: 8093627

Claim:
A nitride semiconductor device comprising: an n-type first layer made of a group III nitride semiconductor; a p-type second layer made of a group III nitride semiconductor with a p-type impurity content of not less than 1×10 18 cm −3 provided on the first layer; an n-type third layer made of a group III nitride semiconductor with a p-type impurity content of not more than 1×10 18 cm −3 provided on the second layer, wherein a group III nitride semiconductor multilayer structure includes the first layer, the second layer and the third layer; a wall surface extending over the first layer, the second layer and the third layer; a gate insulating film formed such that the gate insulating film is opposed to the wall surface; a gate electrode formed such that the gate electrode is opposed to the second layer through the gate insulating film; a drain electrode formed such that the drain electrode is in ohmic contact with the first layer; a source electrode formed such that the source electrode is in ohmic contact with the third layer; and a channel layer, different in conductivity from the second layer, formed on a semiconductor surface portion of the second layer on the wall surface, and having a lower acceptor concentration than the second layer, wherein the gate insulating film is interposed between the channel layer and the gate electrode.