According to one embodiment, a method of manufacturing a semiconductor device includes: forming a first film including a conductive material above a semiconductor substrate; forming a second film on the first film; forming a third film including a conductive material on the second film; exposing a part of the second film; and wet etching the second film. In the wet etching, a first and second insulation films are deposited on side surfaces of the first and third films, and part of a space between the first and third films is blocked by the first and second insulation films to form an air gap between the first and third films.