A method of forming a semiconductor device includes first preliminary holes over an etch target, the first preliminary holes arranged as a plurality of rows in a first direction, forming dielectric patterns each filling one of the first preliminary holes, sequentially forming a barrier layer and a sacrificial layer on the dielectric patterns, forming etch control patterns between the dielectric patterns, forming second preliminary holes by etching the sacrificial layer, each of the second preliminary holes being in a region defined by at least three dielectric patterns adjacent to each other, and etching the etch target layer corresponding to positions of the first and second preliminary holes to form contact holes.