A semiconductor device includes: a semiconductor substrate of the first-type; a semiconductor region of the first-type formed on the substrate; a gate electrode a part of which is present within a trench selectively formed in part of the semiconductor region, and an extended top-end to have a wide width via a stepped-portion; a gate insulating-film formed between the trench and the gate electrode along a wall surface of the trench; a base layer of the second-type on the region via the film to enclose a side-wall except a bottom of the trench; a source region of the first-type adjacent to the film outside the trench in the vicinity of a top surface of the base layer; and an insulating-film formed partially between a bottom-surface of the top-end and a top-surface of the source region and formed to have a thickness larger than that of the gate insulating-film within the trench.