A semiconductor device comprises a semiconductor substrate, an electrically rewritable semiconductor memory cell provided on the semiconductor substrate, the memory cell comprising an island semiconductor portion provided on the surface of the semiconductor substrate or above the semiconductor substrate, a first insulating film provided on a top surface of the island semiconductor portion, a second insulating film provided on a side surface of the island semiconductor portion and being smaller in thickness than the first insulating film, and a charge storage layer provided on the side surface of the island semiconductor portion with the second insulating film interposed therebetween and on a side surface of the first insulating film, a third insulating film provided on the charge storage layer, and a control gate electrode provided on the third insulating film.