A photomask includes a reticle substrate, a main pattern disposed on the reticle substrate and defining a photoresist pattern realized on a semiconductor substrate, and anti-reflection patterns adjacent to the main pattern. A distance between a pair of the anti-reflection patterns adjacent to each other is a first length, and a width of at least one of the pair of anti-reflection patterns is a second length. A sum of the first length and the second length is equal to or smaller than a minimum pitch defined by resolution of an exposure process. A distance between the main pattern and the anti-reflection pattern nearest to the main pattern is equal to or smaller than the first length.