A semiconductor device includes: a fin that is a portion of a semiconductor substrate, protrudes from a main surface of the semiconductor substrate, has a width in a first direction, and extends in a second direction; a control gate electrode that is arranged on the fin via a first gate insulating film and extends in the first direction; and a memory gate electrode that is arranged on the fin via a second gate insulating film and extends in the first direction. Further, a width of the fin in a region in which the memory gate electrode is arranged via the second gate insulating film having a film thickness larger than the first gate insulating film is smaller than a width of the fin in a region in which the control gate electrode is arranged via the first gate insulating film.