A method for fabricating a semiconductor device is provided. The method of fabricating a semiconductor device provides a semiconductor substrate; forming a first insulating layer, a first conductive layer and a chemical mechanical polishing (CMP) stop layer over the semiconductor substrate in sequence; forming openings in the chemical mechanical polishing (CMP) stop layer and the underlying first conductive layer to expose the first insulating layer, thereby leaving a patterned chemical mechanical polishing (CMP) stop layer and a patterned first conductive layer; forming a second insulating layer on the patterned chemical mechanical polishing (CMP) stop layer, filling in the openings; performing a planarization process to remove a portion of the second insulating layer until the patterned chemical mechanical polishing (CMP) stop layer is exposed, thereby leaving a remaining second insulating layer in the openings; removing the patterned chemical mechanical polishing (CMP) stop layer.