A semiconductor device and method of fabricating the same are provided. The method includes: depositing a silicon layer containing amorphous silicon on a substrate; partially crystallizing the amorphous silicon by applying an annealing process to the silicon layer under an atmosphere of H2O at a predetermined temperature; forming a polycrystalline silicon layer by applying an laser annealing process to the partially crystallized amorphous silicon layer; forming a gate insulating layer on the polycrystalline silicon layer; and forming a gate electrode on the gate insulating layer, so that a substrate is prevented from being bent due to high temperature crystallization while the amorphous silicon is crystallized through an SPC process, thereby reducing defects of the thin film transistor.