A mask for crystallizing silicon includes a first, a second, and a third pattern part arranged in a longitudinal direction, each of the first, second, and third pattern parts including a plurality of unit blocks for transmitting and blocking a portion of light. At least two of the first, second and third pattern parts have a corresponding pattern to each other. Advantageously, scans using the aforementioned mask effectively remove a boundary on the silicon formed by the difference in the amount of laser beam irradiation received by the silicon, thereby improving electronic characteristics of the silicon.