To provide a method of manufacturing a semiconductor device which is prevented from degradation of characteristics such as the occurrence of gate leakage current, short-circuits, etc.

The method of manufacturing the semiconductor device includes a process wherein by exposing and developing a resist film using an exposure mask having a phase shifter, the resist film is patterned; a process wherein a third film (polycrystalline silicon film) is selectively dry-etched with a second resist film 118 as a mask, and a second film (silicon oxide film 108) as an etching stopper to process the third film to a first pattern; a process wherein the third film (polycrystalline silicon film 110a) is further dry-etched with the second film as an etching stopper, removing part of the third film, to process the third film to a second pattern; and a process wherein the third film (polycrystalline silicon film 110b) processed to the second pattern is used as a mask.