After crystallization of a semiconductor film is performed by irradiating first laser light (energy density of 400 to 500 mJ/cm.sup.2) in an atmosphere containing oxygen, an oxide film formed by irradiating the first laser light is removed. It is next performed to irradiate second laser light under an atmosphere that does not contain oxygen (at a higher energy density than that of the first laser light irradiation), thus to increase the flatness of the semiconductor film.