A semiconductor device includes a semiconductor layer having a plurality of element regions in its surface area, which are delimited by at least one element isolation trench, a plurality of floating gate electrodes provided on the element regions with a first gate insulation film interposed therebetween and each including a first charge-storage layer having a first width which is equal to that of each of the element regions and a second charge-storage layer stacked on the first charge-storage layer and having a second width which is smaller than the first width, and a plurality of control gate electrodes provided on the floating gate electrodes with a second gate insulation films interposed therebetween. The device further includes an element isolating insulation film buried into the element isolation trench. The top surface of the element isolating insulation film is located higher than that of the first charge-storage layer.