The present invention relates to a method of manufacturing a semiconductor device, and the method uses the mode of thermal annealing the source/drain regions and performing Halo ion implantation to form a Halo ion-implanted region by: first removing the dummy gate to expose the gate dielectric layer to form an opening; then performing a tilted Halo ion implantation to the device from the opening to form a Halo ion-implanted region on both sides of the channel of the semiconductor device; and then annealing to activate the dopants in the Halo ion-implanted region; finally performing subsequent process to the device according to the requirement of the manufacture process. Through the present invention, the dopants in the Halo ion-implanted region improperly introduced to the source region and the drain region may be reduced, and then the overlap between the Halo ion-implantation region and the dopant region of the source/drain regions may be reduced, thus to reduce the band-band leakage current in the MOSFET, and hence improve the performance of the device.