Method for fabricating semiconductor device

According to one embodiment, a method for fabricating a semiconductor device including a memory cell portion and a select gate portion, the method includes etching a charge accumulation layer, a tunnel insulating film, and a semiconductor substrate to make a trench, burying a first insulating film in the trench to contact with a side surface of the charge accumulation layer, performing heat processing to compress the first insulating film, forming a second insulating film on the charge accumulation layer and the first insulating film, etching the second insulating film in the select gate portion to expose a surface of the charge accumulation layer, forming a silicon layer to contact with the exposed surface of the charge accumulation layer, forming a metal layer on the silicon layer, and performing heat processing to silicide an entire boundary region between the charge accumulation layer and the tunnel insulating film.