A method for forming a semiconductor device is provided. The method includes providing a semiconductor substrate, a metal gate stack, and an insulating layer formed over the semiconductor substrate. A source region and a drain region are formed in the semiconductor substrate. The metal gate stack is between the source region and the drain region. The insulating layer surrounds the metal gate stack. The method includes forming contact openings passing through the insulating layer to expose the source region and the drain region, respectively. The method includes performing a first pre-amorphized implantation process to form amorphous regions in the source region and the drain region exposed by the contact openings. The method includes after the first pre-amorphized implantation process, forming a dielectric spacer liner layer over sidewalls of the contact openings. The dielectric spacer liner layer has holes exposing portions of the amorphous regions, respectively.