A method of forming patterns of a semiconductor device includes forming a material film on a substrate, forming a hard mask on the material film, forming a first mold mask pattern and a second mold mask pattern on the hard mask, forming a pair of first spacers to cover opposite sidewalls of the first mold mask pattern, and a pair of second spacers to cover opposite sidewalls of the second mold mask pattern, forming a first gap and a second gap to expose the hard mask by removing the first mold mask pattern and the second mold mask pattern, the first gap being formed between the pair of first spacers and the second gap being formed between the pair of second spacers, forming a mask pattern on the hard mask to cover the first gap and expose the second gap, forming an auxiliary pattern to cover the second gap, removing the mask pattern; and forming a hard mask pattern by patterning the hard mask using the first spacers, the second spacers and the auxiliary pattern as a mask.