laser device 105 can emit either of a continuous laser beam and an intermittent pulse laser beam and can also move back and forth or right and left by a moving means such as servo motors not shown such that the amorphous silicon layer 123 is scanned uniformly the laser device 105 preferably irradiates five to twelve laser beam pulses to a target of the amorphous silicon layer 123 under the control of the laser adjuster 115 the energy of one laser beam pulse is between a complete melting energy and a surface melting energy the complete melting energy which is dependent on a thickness of the silicon layer means the energy that can melt the amorphous silicon layer completely thereby causing no seed of crystal or too many seeds of very tiny sized crystal the surface melting energy means the energy that can melt only the surface of the silicon layer one pulse of the laser beam can satisfy crystallization activation in this embodiment the energy density per pulse is 290 to 400 mj cm2 for an amorphous silicon with a thickness of 600 angstroms when laser annealing is performed in a normal atmosphere for polycrystallization of the amorphous silicon layer the amorphous silicon layer has an oxidation film on a surface thereof due to oxygen existing in the atmosphere when the amorphous silicon layer is heated during polycrystallization such an oxidation film deteriorates the roughness characteristic of grain boundaries leading to bad electric characteristics of the polycrystalline silicon layer in order to overcome this problem the preferred embodiment of the present invention provides a method of adjusting the number of laser shots irradiated.