The present invention is a semiconductor device having a defect blocking region. The semiconductor device includes a substrate, a defect source region, a semiconductor layer and a defect blocking region. The defect source region is on the substrate, wherein the defect source region is a metamorphic buffer layer or a buffer layer, the semiconductor layer over the defect source region, wherein a lattice constant of the semiconductor layer is different from a lattice constant of the substrate. The defect blocking region is disposed on the substrate and below the semiconductor layer, wherein the defect blocking region includes a superlattice structure, wherein at least one of two adjacent layers of the superlattice structure has strain relative to the semiconductor layer, or a lattice constant of the superlattice structure is close to or equal to the lattice constant of the semiconductor layer.