A semiconductor device includes a substrate having first and second regions, a first gate electrode layer on the first region, and including a first conductive layer, and a second gate electrode layer on the second region, and including the first conductive layer, a second conductive layer on the first conductive layer, and a barrier metal layer on the second conductive layer, wherein an upper surface of the first gate electrode layer is at a lower level than an upper surface of the second gate electrode layer.