A method of manufacturing a MOS transistor device is provided. First, a semiconductor substrate having a gate structure is prepared. The gate structure has two sidewalls and a liner on the sidewalls. Subsequently, a stressed cap layer is formed on the semiconductor substrate, and covers the gate structure and the liner. Next, an activating process is performed. Furthermore, the stressed cap layer is etched to be a salicide block. Afterward, a salicide process is performed to form a silicide layer on the regions that are not covered by the stressed cap layer.