To provide a semiconductor device with nonvolatile memory, having improved performance.A memory cell has control and memory gate electrodes on a semiconductor substrate via an insulating film and another insulating film having first, second, and third films stacked one after another in order of mention, respectively. The memory and control gate electrodes are adjacent to each other via the stacked insulating film. The second insulating film has a charge accumulation function. The first and third insulating films each have a band gap greater than that of the second insulating film. An inner angle of the second insulating film between a portion extending between the semiconductor substrate and the memory gate electrode and a portion extending between the control gate electrode and the memory gate electrode is ≧90°. An inner angle of the corner portion between the lower surface and the side surface of the memory gate electrode is