A semiconductor device includes a semiconductor substrate formed with a plurality of first element isolation trenches having respective first opening widths and a plurality of second element isolation trenches having larger opening widths than the first opening widths, element isolation insulating films buried in the first element isolation trenches so that upper parts of the trenches have partial openings, respectively and buried in the second element isolation trenches respectively, and coating type oxide films formed so as to fill the openings of the first element isolation trenches, respectively. The coating-type oxide films are not buried in the second element isolation insulating trenches.