A semiconductor device and a method of manufacturing the same are disclosed. The method includes forming ion impurity regions of a first conductivity type by forming a trench in a semiconductor substrate and implanting impurity ions into a lower portion of the trench at different depths; forming an oxide region in the substrate adjacent to one end of the trench; forming a device isolation film filling the trench; forming a high voltage well in the substrate and a second conductivity type body in the high voltage well; forming a gate on the semiconductor substrate partially overlapping the device isolation film; forming second well in the semiconductor substrate at one side of the device isolation film overlapping the ion diffusion regions and the oxide region; and forming source regions in the body and a drain region in the second well.