A method includes forming a gate stack over a semiconductor substrate, forming a first spacer layer on a sidewall of the gate stack, forming a sacrificial spacer film over the first spacer layer, forming an epitaxy structure on the semiconductor substrate, and performing an etching process on the sacrificial spacer film to form a gap between the first spacer layer and the epitaxy structure. An outer portion of the sacrificial spacer film has a topmost end higher than that of an inner portion of the sacrificial spacer film after performing the etching process. The method further includes forming a second spacer layer to seal the gap between the epitaxy structure and the first spacer layer.