A manufacturing method of a semiconductor device includes: forming step of forming an etching mask on a second main face of a substrate, the etching mask being made of Cu or Cu alloy and having an opening, the second main face being on an opposite side of a first main face of the substrate where a nitride semiconductor layer is provided; a first etching step of applying a dry etching to the second main face of the substrate with use of the etching mask so that all of or a part of the nitride semiconductor layer is left; a removing step of removing the etching mask after the first etching step; and a second etching step of dry-etching the left nitride semiconductor layer after the removing step.