The present disclosure discloses a method of forming a semiconductor layer on a substrate. The method includes patterning the semiconductor layer into a fin structure. The method includes forming a gate dielectric layer and a gate electrode layer over the fin structure. The method includes patterning the gate dielectric layer and the gate electrode layer to form a gate structure in a manner so that the gate structure wraps around a portion of the fin structure. The method includes performing a plurality of implantation processes to form source/drain regions in the fin structure. The plurality of implantation processes are carried out in a manner so that a doping profile across the fin structure is non-uniform, and a first region of the portion of the fin structure that is wrapped around by the gate structure has a lower doping concentration level than other regions of the fin structure.