A semiconductor device including a substrate including a recess; a gate insulation layer on a surface of the recess; a first gate pattern on the gate insulation layer and filling a lower portion of the recess; a second gate pattern on the first gate pattern in the recess and including a material having a work function different from a work function of the first gate pattern; a capping insulation pattern on the second gate pattern and filling an upper portion of the recess; a leakage blocking oxide layer on the gate insulation layer at an upper sidewall of the recess above an upper surface of the first gate pattern and contacting a sidewall of the capping insulation pattern; and impurity regions in the substrate and adjacent to the upper sidewall of the recess, each impurity region having a lower surface higher than the upper surface of the first gate pattern.