The manufacturing a semiconductor device includes providing a substrate supporting a gate electrode, amorphizing and doping the source/drain regions located on both sides of the gate electrode by performing a pre-amorphization implant (PAI) process and implanting C or N into the source/drain regions in or separately from the PAI process, forming a stress inducing layer on the substrate to cover the amorphized source/drain regions, and subsequently recrystallizing the source/drain regions by annealing the substrate. The stress inducing layer may then be removed. Also, the C or N may be implanted into the entirety of the source/drain regions after the regions have been amorphized, or only into upper portions of the amorphized source/drain regions.