A method for fabricating a semiconductor structure. The method includes providing a substrate and forming a plurality of fin structures on the substrate. Each fin structure includes a first side and a second side opposite to the first side. The method further includes forming a first doped region containing first doping ions in a portion of the substrate on the first side of each gate structure, and forming a second doped region containing second doping ions in a portion of the substrate on the second side of each gate structure. The ion concentration of the second doping ions in the second doped region is smaller than the ion concentration of the first doping ions in the first doped region, and the atomic weight of the second doping ions is smaller than the atomic weight of the first doping ions.