In one embodiment, a method of manufacturing a semiconductor device includes alternately forming a plurality of first films and a plurality of second films on a substrate, and forming an opening in the first and second films. The method further includes sequentially forming a first insulator, a charge storage layer, a second insulator and a semiconductor layer on surfaces of the first and second films in the opening. The second insulator includes a silicon oxynitride film, and the silicon oxynitride film is formed using a first gas that includes silicon and a first element, a second gas that includes oxygen and nitrogen, and a third gas that includes a second element that reacts with the first element.