A semiconductor device according to an embodiment of the present invention includes: a semiconductor substrate; an isolation structure formed in a trench, formed in the semiconductor substrate, through a semiconductor oxide film; a floating gate formed on the semiconductor substrate between the isolation structures through an insulating film; a gate oxidation protection film formed on a side surface, on the isolation structure side, of the floating gate so that each of a part of a side surface and a bottom surface of the gate oxidation protection film contacts the insulating film; and a control gate formed on the floating gate through an inter-gate insulating film.