A method for manufacturing a thin film transistor with improved current characteristics and high electron mobility. According to the method, when an amorphous silicon thin film is crystallized into a polycrystalline silicon thin film by metal-induced crystallization, annealing conditions of the amorphous silicon thin film and the amount of a metal catalyst doped into the amorphous silicon thin film are optimized to reduce the regions of a metal silicide distributed at grain boundaries of the polycrystalline silicon thin film. In addition, oxygen (O2) gas or water (H2O) vapor is supplied to form a passivation film on the surface of the polycrystalline silicon thin film.