The present application discloses a semiconductor device and a method for forming the same. The method comprises: providing a first semiconductor layer and forming a first STI in the first semiconductor layer; determining a selected region in the first semiconductor layer, and making a portion of the first semiconductor layer in the selected region recessed; and in the selected region, epitaxially growing a second semiconductor layer on the first semiconductor layer, wherein the material of the second semiconductor layer is different from that of the first semiconductor layer. According to the present invention, a structure with a second semiconductor layer selectively epitaxially grown and embedded in the first semiconductor layer can be formed by a simple process, and defects generated during the epitaxial growth process can be further reduced.