A method of fabricating a semiconductor device includes epitaxially-growing a strained material in a cavity of a substrate comprising a major surface and the cavity, the cavity being below the major surface. A lattice constant of the strained material is different from a lattice constant of the substrate. The method also includes forming a first metal layer over the strained material, and forming a dielectric layer over the first metal layer, wherein the dielectric layer has a thickness ranging from 1 nm to 10 nm. The method further includes forming a dummy poly-silicon over the dielectric layer, and forming an interlayered dielectric layer (ILD) surrounding the dummy poly-silicon. The method additionally includes removing the dummy poly-silicon over the dielectric layer, and forming a second metal layer over the dielectric layer.