A semiconductor device is disclosed which includes a silicide substrate, a nitride layer, two STIs, and a strain nitride. The silicide substrate has two doping areas. The nitride layer is deposited on the silicide substrate. The silicide substrate and the nitride layer have a recess running through. The two doping areas are at two sides of the recess. The end of the recess has an etching space bigger than the recess. The top of the silicide substrate has a fin-shaped structure. The two STIs are at the two opposite sides of the silicide substrate (recess). The strain nitride is spacer-formed in the recess and attached to the side wall of the silicide substrate, nitride layer, two STIs. The two doping areas cover the strain nitride. As a result, the efficiency of semiconductor is improved, and the drive current is increased.