The invention discloses a semiconductor device and a manufacturing method thereof. The method for manufacturing the semiconductor device comprises the steps of providing a substrate, wherein the substrate comprises a cavity array, each side surface of a cavity is consistent with one lateral crystal face of a crystal in direction; forming a buffer layer at the surface of the substrate, wherein a material of the buffer layer fills the cavity; and forming a fin-type channel layer at the surface of the buffer layer. Because the independently grown crystals are provided with lateral crystal faces, the dislocation defect density is significantly reduced, and the performance of the device can be greatly improved.