A sequential lateral solidification device and a method of crystallizing silicon using the same controls a size and arrangement overlapping areas of laser beam patterns adjacently irradiated onto a substrate to within specific regions of a pixel area and a driving area outside the pixel area. The device includes a laser generating device irradiating a laser beam, a focusing lens focusing the laser beam, a mask having a pattern of transparent regions permitting the laser beam to be transmitted a laser beam pattern, a reduction lens reducing the laser beam pattern transmitted by the mask, a substrate having a pixel area and a driving area exposed to the irradiated laser beam pattern, a moveable stage having, on which the substrate is mounted, and a position sensor sensing an position of the irradiated laser beam pattern and controlling a size and arrangement overlapping areas between adjacently irradiated laser beam patterns.