METHOD OF MANUFACTURING SEMICONDUCTOR STORAGE DEVICE AND SEMICONDUCTOR STORAGE DEVICE

Method of manufacturing a semiconductor device includes forming, in a first region, a first trench through a second gate electrode film and an interelectrode insulating film, and a second trench partially extending into a sacrificial film in an isolation trench, filling the second trench with a first insulating film; forming a third gate electrode film above the second gate electrode film and into the first trench such that the third gate electrode film contacts the first gate electrode film; etching the third and the second gate electrode film, the interelectrode insulating film, and the first gate electrode film to form select gate electrodes in the first region and a group of memory-cell gate electrodes in the second region; removing the sacrificial film; and forming a second insulating film over the element regions and the isolation trench to define an unfilled gap in the isolation trench below the memory-cell gate electrodes.