A semiconductor device including a Si (110) substrate, a buffer layer, a first type doped semiconductor layer, a light-emitting layer and a second type doped semiconductor layer is provided. The Si (110) substrate has a plurality of trenches. Each trench at least extends along a first direction, and the first direction is parallel to a <1-10> crystal direction of the Si (110) substrate. The buffer layer is located on the Si (110) substrate and exposes the trenches. The first type doped semiconductor layer is located on the buffer layer and covers the trenches. The light-emitting layer is located on the first type doped semiconductor layer. The second type doped semiconductor layer is located on the light-emitting layer. A fabrication method of a semiconductor device is also provided.