The performances of a semiconductor device are improved. In a method for manufacturing a semiconductor device, a first insulation film, a conductive film, a silicon-containing second insulation film, and a third film formed of silicon are sequentially formed at the surface of a control gate electrode. Then, the third film is etched back to leave the third film at the side surface of the control gate electrode via the first insulation film, the conductive film, and the second insulation film, thereby to form a spacer. Then, the conductive film is etched back to form a memory gate electrode formed of the conductive film between the spacer and the control gate electrode, and between the spacer and the semiconductor substrate.