Manufacturing stability of a semiconductor device is improved. A method of manufacturing a semiconductor device includes the steps of: forming an etching stopper film over a first interlayer insulating film; forming an inorganic insulating film over the etching stopper film; forming a resist film over the inorganic insulating film; selectively etching the etching stopper film and the inorganic insulating film by using the resist film as a mask to form a first opening in the etching stopper film and to form a second opening in the inorganic insulating film; removing the resist film by O2 plasma ashing; forming a second interlayer insulating film over the inorganic insulating film; and etching the second interlayer insulating film to form a wiring groove that is coupled to the second opening, and etching a portion located under the first opening of the first interlayer insulating film to form a via hole.