A method of manufacturing a semiconductor device having a first memory cell array region and a second memory cell array region, the method includes forming an active region on a surface layer of a semiconductor substrate, forming a first word line extending in a first direction on the gate insulating film in the first memory cell array region, and forming a second word line extending in a second direction crossing the first direction on the gate insulating film in the second memory cell array region, wherein the ion implantation into the active region is performed from a direction that is inclined from a direction vertical to the surface of the semiconductor substrate and is oblique with respect to both the first direction and the second direction.