Embodiments relate to a method of decomposing a layout of a semiconductor device. The method may include generating a pattern layout including first patterns and second patterns, generating an interference map for the pattern layout, the interference map including optical interference information regarding the first and second patterns, and decomposing the pattern layout into a first decomposition pattern layout including the first patterns, and a second decomposition pattern layout including the second patterns, based on the interference map. In the interference map, an influence of constructive interference on the first patterns may be greater than an influence of constructive interference on the second patterns.