There is provided a method for manufacturing a crystalline semiconductor film. An insulating film is formed over a substrate; an amorphous semiconductor film is formed over the insulating film; a cap film is formed over the amorphous semiconductor film; the amorphous semiconductor film is scanned and irradiated with a continuous wave laser beam or a laser beam with a repetition rate of greater than or equal to 10 MHz, through the cap film; and the amorphous semiconductor film is melted and crystallized. At that time, an energy period in a length direction in a laser beam spot of the laser beam is 0.5 .mu.m to 10 .mu.m, preferably, 1 .mu.m to 5 .mu.m; an energy distribution in a width direction in a laser beam spot of the laser beam is a Gaussian distribution; and the amorphous semiconductor film is scanned with the laser beam so as to be irradiated with the laser beam for a period of greater than or equal to 5 microseconds and less than or equal to 100 microseconds per region.