Abstract: Disclosed herein is an effective method of annealing a semiconductor film by irradiation with a laser light. This method consists of irradiating an amorphous silicon film 102 formed on a glass substrate 110 with a linear laser light 100 which is relatively scanned in the direction of arrow 109. The area which will soon be or has just been irradiated with a laser light is heated by heaters 105 and 106. Irradiation in this way crystallizes the amorphous silicon film 102 without abrupt phase change which otherwise occurs due to laser light irradiation.