The instant disclosure discloses a semiconductor device comprising a substrate having a cell region; a device layer over the substrate; a plurality of capacitor lower electrodes over the device layer in the cell region, each of the capacitor lower electrodes has a U-shaped profile defining an inner surface in a cross section; a capacitor dielectric liner on the inner surfaces of the capacitor lower electrodes; and a SiGe layer over the capacitor dielectric liner, wherein the SiGe layer has a Ge concentration distribution that has a greatest value at a middle portion of the SiGe layer and decreases there-from upwardly and downwardly along a thickness direction.