PURPOSE: To obtain the manufacturing method of a MOS semiconductor device having a DI-LDD structure in which the fluctuation of the threshold or deterioration of the current driving ability is suppressed or a pocket structure.

CONSTITUTION: The title method involves a process for forming a gate insulating film 3 on a P-type semiconductor substrate 1 and P-type channel impurity area 4 in a channel area, process for forming a gate electrode 5 and N-type low- concentration LDD diffusion layer 6 by using the electrode 5 as a mask, process for forming side walls 7 on both sides of the electrode 5 and P-type punch- through stopper areas 8 by using the walls 7 as masks, and process for forming an N-type high-concentration source-drain areas 9. Since the side walls 7 are utilized for injection at the time of forming the stopper areas 8, the influence of the areas 8 to the impurity area 4 can be prevented and the fluctuation of the threshold or deterioration of the current driving ability can be prevented.