A semiconductor device having a dual gate electrode and a method of forming the same are provided. The semiconductor device includes a substrate including first and second regions. A first gate electrode formed of a first metal silicide is disposed on the substrate of the first region. A second gate electrode is disposed on the substrate of the second region. The second gate electrode is formed of a second metal silicide including a metal the same as that of the first metal silicide. A gate insulating layer is interposed between the substrate and the first gate electrode, and between the substrate and the second gate electrode. The gate insulating layer brings about a Fermi pinning effect increasing or decreasing intrinsic work functions of the first and second metal silicides. In this case, the first metal silicide is a lower silicon concentration than the second metal silicide so that the Fermi pinning effect provided to the first gate electrode is less effective than that provided to the second gate electrode.