A mask includes a base substrate, and a light shielding pattern including a light transmitting portion and a light shielding portion on the base substrate, wherein the light shielding portion includes a third source electrode portion, a third drain electrode portion spaced apart from the third source electrode portion and including at least a portion parallel to the third source electrode portion, a first auxiliary light shielding portion at an end portion of the third source electrode portion facing the third drain electrode portion, and a second auxiliary light shielding portion at an end portion of the third drain electrode portion facing the third source electrode portion.