A mask includes a transparent substrate, a light-blocking layer and a halftone layer. The light-blocking layer includes a source electrode pattern portion including a first electrode portion, a second electrode portion and a third electrode portion, and a drain electrode pattern portion disposed between the second electrode portion and the third electrode portion. The halftone layer includes a halftone portion corresponding to a spaced-apart portion between the source electrode pattern portion and the drain electrode pattern portion, and a dummy halftone portion more protrusive than ends of the second electrode portion and the third electrode portion. Thus, a photoresist pattern corresponding to a channel portion of a thin film transistor (TFT) may be formed with a uniform thickness, to thereby prevent an excessive etching of the channel portion.