The invention discloses a semiconductor device and a manufacturing method thereof. The semiconductor device is formed on a silicon on insulator (SOI) substrate; the SOI substrate comprises a buried insulation layer and a semiconductor layer which is formed on the buried insulation layer; a fin made of a semiconductor material is formed in the semiconductor layer; the fin comprises two opposite side surfaces which are vertical to the surface of the SOI substrate; the semiconductor device comprises a source region and a drain region which are arranged at both ends of the fin, a channel region which is arranged in the middle of the fin and laminations of a grid electrode dielectric and a grid electrode conductor arranged on one side surface of the fin, wherein the grid electrode conductor and the channel region are isolated by the grid electrode dielectric, and the grid electrode conductor extends by deviating from one side surface of the fin along the direction of being parallel with the surface of the SOI substrate. The semiconductor device reduces the short channel effect and decreases the parasitic capacitance and the parasitic resistance, thereby being beneficial to reducing the dimensions of a transistor and improving the performance of the transistor.