The present invention discloses a semiconductor device and a formation method thereof. The device includes a gate structure disposed on a semiconductor substrate, sidewall spacers disposed on the sidewalls of the gate structure, lightly doped source/drain regions which are formed in the semiconductor substrate and located at two sides of the gate structure respectively, source/drain regions whichare formed in the semiconductor substrate and are located at two sides of the sidewall spacers respectively, halo implant regions which are formed in the semiconductor substrate below the gate structure and are adjacent to the lightly doped source/drain regions, and counter-doping regions which are formed in the semiconductor substrate below the gate structure and are located between the lightly doped source/drain regions and the halo implant regions, wherein the doping concentration of the counter-doping regions is lower than the doping concentration of the halo implant regions.