A method of semiconductor fabrication including forming a first work function metal layer on a first region of the substrate and forming a metal layer on the first work function metal layer and on a second region of the substrate. A dummy layer is formed on the metal layer. The layers are then patterned to form a first gate structure in the first region and a second gate structure in the second region of the substrate. The dummy layer is then removed to expose the metal layer, which is treated. The treatment may be an oxygen treatment that allows the metal layer to function as a second work function layer.