By melting amorphous silicon layers on glass by the beam of an Ar+ laser, large grained polycrystalline films as well as single crystalline regions at predefined positions were generated. If the layers are crystallized by scanning a circular laser beam at a rate of up to 5 cm/s the crystal size depends on the overlap between successive scanning traces. The lateral dimensions of the crystals exceed several 10 mu m for an overlap slightly above 50%. Crystals with size dimensions of about 100 mu m were produced by line scanning of a focused laser beam. Large single crystals were obtained by scanning a sickle-shaped or L-shaped beam profile. If the laser is switched on and off repeatedly, single crystalline regions are produced at predefined positions.