A method of forming a pattern of a semiconductor device includes forming a mask and a sacrificial layer on a substrate, etching the sacrificial layer in a first area of the substrate to form first units, each having a first width and a first distance from an adjacent unit, etching the sacrificial layer in a second area of the substrate to form second units, each having a second width equal to the first distance and being spaced apart from an adjacent unit by a second distance equal to the first width, forming a spacer conformally covering the first and second units, the spacer having a first thickness and being merged between the second units, removing a portion of the spacer on upper surfaces of the first and second units, and etching the mask in a region from which first and second units have been removed.