A nonvolatile semiconductor storage device includes a memory string including a plurality of memory cells connected in series with each other, and a select gate transistor connected to a first end of the memory string. The film thickness of a first hard mask on a select gate electrode of the select gate transistor is greater than the film thickness of a second hard mask film on a control gate electrode of the memory cells. The level of an upper surface of a first side wall insulating film provided on a side surface of the select gate transistor is higher than the level of an upper surface of the first hard mask film. The level of an upper surface of a second side wall insulating film provided on a side surface of the memory cells is higher than the level of an upper surface of the second hard mask film.