The invention provides a method for producing a semiconductor device that can reduce the number of mask steps. In a CMOS production process, gate electrodes are formed in regions for forming an NMOS and a PMOS at the same time with a common mask pattern, and after the gate electrodes have been formed, a well, and source and drain regions are formed by impurity ion implantations with a common mask pattern in each region of the NMOS and the PMOS, using the gate electrode as a mask, whereby the number of mask steps is reduced.