A crystalline semiconductor having an even surface and a large crystal grain size is formed on an economical glass substrate using a laser crystallizing technology. A series of processes, including forming an insulation film on a glass substrate; forming a semiconductor film in the first layer; crystallizing the semiconductor film in the first layer by irradiating laser light stepwise from weak energy laser light to strong energy laser light; forming a semiconductor film in a second layer having a film thickness thinner than that of the semiconductor film in the first layer; performing laser crystallization of the semiconductor thin film in the second layer by irradiating laser light stepwise from weak energy laser light to strong energy laser light, are continuously performed without exposing the workpiece to the atmosphere.