A semiconductor device includes a semiconductor substrate including a first driving transistor region having a first driving transistor disposed therein and a second driving transistor region having a second driving transistor disposed therein, wherein the second driving transistor is driven at a lower voltage than the first driving transistor, a first gate insulating layer formed at edges of the second driving transistor region, and a second gate insulating layer formed at a center of the second driving transistor region, wherein the first gate insulating layer is thicker than the second gate insulating layer.