A method of manufacturing a semiconductor device that includes a semiconductor substrate is provided. The method includes: exposing a photoresist coated on the semiconductor substrate using a photomask including a plurality of regions having different light transmittances; developing the photoresist to form a resist pattern including a plurality of regions having different thicknesses that depend on an exposure amount of the photoresist; and implanting impurity ions into the semiconductor substrate through the plurality of regions of the resist pattern having different thicknesses to form a plurality of impurity regions whose depths from a surface of the semiconductor substrate to peak positions are different from each other. The depths to the peak positions depend on the thickness of the resist pattern through which the implanted impurity ions pass.