An improvement is achieved in the performance of a semiconductor device. In a method of manufacturing the semiconductor device, using a control gate electrode and a memory gate electrode which are formed over a semiconductor substrate as a mask, n-type impurity ions are implanted from a direction perpendicular to a main surface of the semiconductor substrate. Then, using the control gate electrode, the memory gate electrode, and first and second sidewall spacers as a mask, other n-type impurity ions are implanted from a direction inclined relative to the direction perpendicular to the main surface of the semiconductor substrate.