A method for fabricating an integrated circuit device is disclosed. An exemplary method includes providing a substrate; forming a high-k dielectric layer over the substrate; forming a first capping layer over the high-k dielectric layer; forming a second capping layer over the first capping layer; forming a dummy gate layer over the second capping layer; performing a patterning process to form a gate stack including the high-k dielectric layer, first and second capping layers, and dummy gate layer; removing the dummy gate layer from the gate stack, thereby forming an opening that exposes the second capping layer; and filling the opening with a first metal layer over the exposed second capping layer and a second metal layer over the first metal layer, wherein the first metal layer is different from the second metal layer and has a work function suitable to the semiconductor device.