To provide a semiconductor device having improved reliability. A semiconductor device is provided forming a control gate electrode for memory cell on a semiconductor substrate via a first insulating film; forming a memory gate electrode for memory cell, which is adjacent to the control gate electrode, on the semiconductor substrate via a second insulating film having a charge storage portion; forming n− type semiconductor regions for source or drain in the semiconductor substrate by ion implantation; forming sidewall spacers on the side wall of the control gate electrode and the memory gate electrode; forming n+ type semiconductor regions for source or drain in the semiconductor substrate by ion implantation; and removing an upper portion of the second insulating film present between the control gate electrode and the memory gate electrode. A removal length of the second insulating film is larger than the depth of the n+ type semiconductor regions.