A method of fabricating a semiconductor device includes forming a photoresist layer on a lower structure to have a first thickness, exposing a portion of the photoresist layer to form an exposed portion and a non-exposed portion of the photoresist layer, removing a part of the photoresist layer to form a photoresist layer having a second thickness that smaller than the first thickness, and removing the exposed portion or the non-exposed portion of the photoresist layer having the second thickness to form a photoresist pattern.