A semiconductor device is obtained in which a first insulating film for a gate insulating film of a memory element is formed over a semiconductor substrate in a memory region, a second insulating film for a gate insulating film of a lower-breakdown-voltage MISFET is formed over the semiconductor substrate in a lower-breakdown-voltage MISFET formation region, and a third insulating film for a gate insulating film of a higher-breakdown-voltage MISFET is formed over the semiconductor substrate in a higher-breakdown-voltage MISFET formation region. Subsequently, a film for gate electrodes is formed and then patterned to form the respective gate electrodes of the memory element, the lower-breakdown-voltage MISFET, and the higher-breakdown-voltage MISFET. The step of forming the second insulating film is performed after the step of forming the first insulating film. The step of forming the third insulating film is performed before the step of forming the first insulating film.