The present invention provides a semiconductor device, including a substrate, a first semiconductor layer, a plurality of first sub recess, a plurality of insulation structures and a first top semiconductor layer. The substrate has a first region disposed within an STI. The first semiconductor layer is disposed in the first region. The first sub recesses are disposed in the first semiconductor layer. The insulation structures are disposed on the first semiconductor layer. The first top semiconductor layer forms a plurality of fin structures, which are embedded in the first sub recesses, arranged alternatively with the insulation structures and protruding over the insulation structures.