A first insulating film is formed on a semiconductor substrate in each of a first region in which a memory transistor is to be formed, a second region in which a selection transistor is to be formed, a third region in which a high-withstand-voltage transistor is to be formed, and a fourth region in which a low-withstand-voltage transistor is to be formed. Subsequently, the first insulating film in each of the first and second regions is removed. A second insulating film is formed on the semiconductor substrate in each of the first and second regions. A third insulating film having a trap level is formed on the second insulating film. The third insulating film in the second region and the second insulating film in the second region are removed. A fourth insulating film is formed on the third insulating film and on the semiconductor substrate in the second region.