Methods for fabricating semiconductor devices are provided. Gate structures are formed on a top surface of a substrate to form semiconductor devices. Trenches are formed in the substrate on both sides of each gate structure of each semiconductor device. The trenches on the both sides of each gate structure are filled with stress layers, the stress layers in the substrate protruding over the top surface of the substrate. The stress layers are ion-doped and annealed on the both sides of each gate structure, and are pulse-etched to form a source region and a drain region of each gate structure. The pulse-etching is controlled such that the source regions and the drain regions of the plurality of semiconductor devices have a top surface coplanar with the top surface of the substrate.