A method of fabricating a semiconductor device by the use of laser crystallization steps is provided. During these crystallization steps, an amorphous or polycrystalline semiconductor is crystallized by laser irradiation in such a way that generation of ridges is suppressed. Two separate laser crystallization steps are carried out. First, a laser irradiation step is performed in a vacuum, using somewhat weak laser light. Then, another laser irradiation step is performed in a vacuum, in the atmosphere, or in an oxygen ambient with intenser laser light. The first laser irradiation conducted in a vacuum does not result in satisfactory crystallization. However, this irradiation can suppress generation of ridges. The second laser irradiation step is performed in a vacuum, in the atmosphere, or in an oxygen ambient to achieve sufficient crystallization, but no ridges are produced.