A semiconductor device of the present invention has a first insulating film formed between a control gate electrode and a semiconductor substrate and a second insulating film formed between a memory gate electrode and the semiconductor substrate and between the control gate electrode and the memory gate electrode, the second insulating film having a charge accumulating part therein. The second insulating film has a first film, a second film serving as a charge accumulating part disposed on the first film, and a third film disposed on the second film. The third film has a sidewall film positioned between the control gate electrode and the memory gate electrode and a deposited film positioned between the memory gate electrode and the semiconductor substrate. In this structure, the distance at a corner part of the second insulating film can be increased, and electric-field concentration can be reduced.