A photomask includes; a source electrode pattern including; a first electrode portion which extends in a first direction, a second electrode portion which extends in the first direction and is substantially parallel to the first electrode portion, and a third electrode portion which extends from a first end of the first electrode portion to a first end of the second electrode portion and is rounded with a first curvature, a drain electrode pattern which extends in the first direction and is disposed between the first electrode portion and the second electrode portion, wherein an end of the drain electrode pattern is rounded to correspond to the third electrode portion; and a channel region pattern which is disposed between the source electrode pattern and the drain electrode pattern, wherein a center location of the first curvature and a center location of the rounded portion of the end of the drain electrode pattern are the same.