In one embodiment, a semiconductor device has a topmost or highest conductive layer with at least one opening. The semiconductor device includes a semiconductor substrate having a cell array region and an interlayer insulating layer covering the substrate having the cell array region. The topmost conductive layer is disposed on the interlayer insulating layer in the cell array region. The topmost conductive layer has at least one opening. A method of fabricating the semiconductor device is also provided. The openings penetrating the topmost metal layer help hydrogen atoms reach the interfaces of gate insulating layers of cell MOS transistors and/or peripheral MOS transistors during a metal alloy process, thereby improve a performance (production yield and/or refresh characteristics) of a memory device.