A semiconductor device and a method for fabricating the same are disclosed. In the method, a substrate structure is provided, including a substrate and a fin-shaped buffer layer formed on the surface of the substrate. A QW material layer is formed on the surface of the fin-shaped buffer layer. A barrier material layer is formed on the QW material layer. The QW material layer is suitable for forming an electron gas therein. Thereby the short-channel effect is improved, while high mobility of the semiconductor device is guaranteed. In addition, according to the present disclosure, thermal dissipation of the semiconductor device may be improved, and thus performance and stability of the device may be improved.