The method for manufacturing comprises an ion implantation process of implanting a p-type impurity into a semiconductor layer mainly made of a group III nitride by ion implantation; a first heating process of heating the semiconductor layer at a first temperature in a first atmospheric gas including ammonia (NH3) after the ion implantation process; and a second heating process of heating the semiconductor layer, after the first heating process, at a second temperature that is lower than the first temperature in a second atmospheric gas including oxygen (O2).