The present disclosure provides an integrated circuit having metal gate stacks. The integrated circuit includes a semiconductor substrate; a gate stack disposed on the semiconductor substrate, wherein the gate stack includes a high k dielectric layer and a first metal layer disposed on the high k dielectric layer; and a raised source/drain region configured on a side of the gate stack and formed by an epitaxy process, wherein the semiconductor substrate includes a silicon germanium (SiGe) feature underlying the raised source/drain region.