A method for forming metal gates is provided. In the method, a substrate with a first region and a second region is provided. Dummy gate structures and an ILD layer is formed on the substrate. Dummy gates of the dummy gate structures are removed to form openings respectively within the two regions. Work function layers are respectively formed to overlay the openings. A metal layer is formed on the work function layers and then a CMP process is performed until the ILD layer is exposed, thereby forming the metal gates within the two regions at the same time. Only one CMP process is performed to the metal layer, so that over polishing of the ILD layer may be reduced and thickness of metal gates may be more accurately controlled.