A semiconductor device includes first and second gate structures over a substrate, the first gate structure has a first width that is smaller than a second width of the second gate structure, in which a lower portion of the first gate structure having a first work-function material (WFM) layer, the first WFM layer having a top surface, a lower portion of the second gate structure having a second WFM layer, the second WFM layer having a top surface. A first gate electrode is disposed over the first WFM layer and a second gate electrode has a lower portion disposed in the second WFM layer, in which the first gate electrode has a first width that is smaller than a second width of the second gate electrode, and wherein the top surface of the second WFM layer is at a level below a top surface of the second gate electrode.