A method for fabricating a semiconductor device is provided. A fin of a first conductivity type is formed on a substrate of the first conductivity type. A gate is formed on the substrate, wherein the gate covers a portion of the fin. Source and drain regions of a second conductivity type are formed in the fin at respective sides of the gate. A punch-through stopper (PTS) of the first conductivity type is formed in the fin underlying the gate and between the source and drain regions, wherein the PTS has an impurity concentration higher than that of the substrate. A first impurity of the second conductivity type is implanted into the PTS, so as to compensate the impurity concentration of the PTS.