A method of crystallizing amorphous silicon using a metal catalyst. More specifically, the method includes forming an amorphous silicon layer over a substrate, forming a plurality of metal clusters on the amorphous silicon film, forming a heat insulating layer on the amorphous silicon layer including the metal clusters, disposing a pair of electrodes on the heat insulating layer, simultaneously applying a thermal treatment and a voltage to crystallize the amorphous silicon, and removing the heat insulating layer including the electrodes from the substrate.