To provide a method for manufacturing a semiconductor device in which the unevenness of ON current, mobility or a threshold value of a TFT can be suppressed by suppressing the occurrence of the uneven state of the surface of a semiconductor film or crystallinity, and to provide the semiconductor device manufactured by using this manufacturing method.

The method for manufacturing the semiconductor device includes the steps of adding a rare gas to the semiconductor film formed on the surface of an insulator by using an ion doping method, and irradiating the semiconductor film in which the rare gas is added with a laser beam of a pulse oscillation in a rare gas atmosphere. In the case of irradiating with the laser beam, a vibration by an ultrasonic wave may be imparted to the semiconductor film in which the rare gas is added.