Disclosed are a photomask, an exposure apparatus, and a method of fabricating a three-dimensional semiconductor memory device using the same. The photomask may include a mask substrate, a first mask pattern on the mask substrate, and an optical path modulation substrate. The optical path modulation substrate may include a first region on a portion of the first mask pattern, and a second region on another portion of the first mask pattern. The second region has a thickness that is less than a thickness of the first region.