A method of forming a polycrystalline semiconductor layer includes forming a semiconductor layer of amorphous silicon on a substrate, forming a plurality of spot seeds in the semiconductor layer by irradiating a first laser beam through a crystallization mask, each of the plurality of spot seeds being equally spaced from one another and each having equal area, and forming a polycrystalline silicon layer along an entire surface of the substrate by irradiating a second laser beam onto the semiconductor layer.