Nitride semiconductor device

A method for manufacturing a nitride semiconductor device comprising:

• a first step of forming a first nitride semiconductor layer that constitutes an electron transit layer, a second nitride semiconductor layer that constitutes an electron supply layer, and a nitride semiconductor gate layer material film that contains an acceptor type impurity in that order on a substrate;
• a second step of forming a gate electrode film that is a material film of a gate electrode on the nitride semiconductor gate layer material film;
• a third step of patterning the gate electrode film and the nitride semiconductor gate layer material film by etching to form a nitride semiconductor gate layer that has a pair of mutually parallel ridge portions and a ridge coupling portion coupling corresponding end portions thereof to each other and a gate electrode that has a gate principal electrode portion formed on the ridge portions;
• and a fourth step of forming, on the electron supply layer, a source electrode that includes a source principal electrode portion disposed inside a region between the pair of ridge portions such as to be parallel to the ridge portions and at the same time forming a drain electrode that includes a drain principal electrode portion disposed inside a region at an outer side of the pair of ridge portions such as to be parallel to the ridge portions;
• and wherein a length direction of the ridge portions is a [110] direction of a semiconductor crystal structure that constitutes the second nitride semiconductor layer.