A semiconductor storage device has a semiconductor substrate, a plurality of first insulating films formed on the semiconductor substrate with predetermined spacing therebetween, an element isolation region formed between the first insulating films in a first direction, a floating gate electrode comprising a first charge accumulation film formed on the first insulating film, a second charge accumulation film formed on the first charge accumulation film and having a width in a second direction orthogonal to the first direction smaller than the width of the first charge accumulation film, and a third charge accumulation film formed on the second charge accumulation film and having the width in the second direction larger than the width of the second charge accumulation film, a second insulating film formed on the second charge accumulation film and between the second charge accumulation film and the element isolation region, a third insulating film formed on the charge accumulation film and the element isolation region along the second direction, and a control gate electrode formed on the third insulating film.