A lamination pattern having a control gate electrode, a first insulation film thereover, and a second insulation film thereover is formed over a semiconductor substrate. A memory gate electrode is formed adjacent to the lamination pattern. A gate insulation film is formed between the control gate and the semiconductor substrate. A fourth insulation film, including a lamination film of a silicon oxide film, a silicon nitride film, and another silicon oxide film, is formed between the memory gate electrode and the semiconductor substrate and between the lamination pattern and the memory gate electrode. At the sidewall on the side of the lamination pattern adjacent to the memory gate electrode, the first insulation film is retreated from the control gate electrode and the second insulation film, and the upper end corner portion of the control gate electrode is rounded.