Abstract: A semiconductor device includes a stressor. A device isolation layer is formed on a substrate to define an active region. A gate electrode is formed on the active region. A trench is formed in the active region adjacent to the gate electrode and has first and second sidewalls. A stressor is formed within the trench. The first sidewall of the trench is near the gate electrode and relatively far away from the device isolation layer. The second sidewall of the trench is near the device isolation layer and relatively far away from the gate electrode. The second sidewall of the trench has a step shape.