Over a semiconductor substrate, a memory gate electrode for a nonvolatile memory cell is formed via a first insulating film having an internal charge storage portion. A dummy control gate electrode is formed so as to be adjacent to the memory gate electrode via a second insulating film. The memory and the dummy control gate electrodes are made of different materials. A third insulating film is formed so as to cover the memory and the dummy control gate electrodes and then polished to expose the memory and the dummy control gate electrodes. Then, etching is performed under a condition in which the memory gate electrode is less likely to be etched than the dummy control gate electrode to remove the dummy control gate electrode. Then, in a trench as a region from which the dummy control gate electrode is removed, a control gate electrode for the memory cell is formed.