A semiconductor device includes a substrate with a recess pattern, a gate electrode filling the recess pattern, a threshold voltage adjusting layer formed in the substrate under the recess pattern, a source/drain region formed in the substrate on both sides of the gate electrode and a gate insulation layer, with the recess pattern being disposed between the gate electrode and the substrate, wherein the thickness of the gate insulation layer formed in a region adjacent to the source/drain region is greater than the thickness of the gate insulation layer formed in a region adjacent to the threshold voltage adjusting layer.