Methods of forming contact holes include forming a first guide pattern over an etching target layer. The first guide pattern has first openings each extending in a first direction and each first opening arranged in a direction perpendicular to the first direction. A first BCP structure is formed in each first opening. The first BCP structure includes first material layers in the first direction at a first pitch in each of the first openings, and second material layers filling a remaining portion of each first opening. First holes are formed by removing the first material layers. A second guide pattern is formed over the first guide pattern and the second material layers, and the above processes are performed on the second guide pattern to form second holes. Portions of the etching target layer overlapped by the first holes or the second holes are removed to form a desired pattern.