A semiconductor device includes: a semiconductor layer having a main surface; a first conductive type well region formed on a surface portion of the main surface of the semiconductor layer; a second conductive type source region formed on a surface portion of the well region; a second conductive type drain region formed on the surface portion of the well region at an interval from the source region; a planar gate structure formed on the main surface of the semiconductor layer so as to face a first conductive type channel region disposed between the source region and the drain region; and a memory structure disposed adjacent to a lateral side of the planar gate structure, and including an insulating film formed on the channel region and a charge storage film facing the channel region with the insulating film interposed between the charge storage film and the channel region.