A method of fabricating a semiconductor device includes providing a semiconductor substrate having a first active region and a second active region, forming a first metal layer over a high-k dielectric layer, removing at least a portion of the first metal layer in the second active region, forming a second metal layer on first metal layer in the first active region and over the high-k dielectric layer in the second active region, and thereafter, forming a silicon layer over the second metal layer. The method further includes removing the silicon layer from the first gate stack thereby forming a first trench and from the second gate stack thereby forming a second trench, and forming a third metal layer over the second metal layer in the first trench and over the second metal layer in the second trench.