In a method of manufacturing a semiconductor device including independent gate patterns separated from each other, an active region is defined by forming a field region on a substrate. A gate oxide layer and a polysilicon layer are formed on the substrate. A preliminary gate pattern is formed by partially removing the polysilicon layer along a first direction by a first etching process. A spacer is formed along a side surface of the preliminary gate pattern. A number of separated gate patterns is formed by partially removing the preliminary gate pattern along a second direction crossing the first direction by a second etching process. The gate patterns overlap with the active regions and are separated from each other. Therefore, the overlap margin is increased, and the polysilicon layer is prevented from being over-etched when it is patterned to form the gate pattern.