Method of manufacturing semiconductor device

In a method of manufacturing a semiconductor device, an initial pattern layout is obtained. The initial pattern layout incudes fin patterns which include active fin patterns to be formed as active fin structures and dummy fin patterns not to be formed as actual fin structures or to be removed. The locations of the fin patterns are modified, as follows. A space between adjacent active fin patterns is increased by a first amount, a space between the dummy fin patterns is decreased by a second amount, and a space between one of the dummy fin patterns and one of the active fin patterns adjacent to the one of the dummy fin patterns is decreased by a third amount. Mandrel patterns are placed so that the fin patterns of which locations are modified are placed along longitudinal edges of the mandrel patterns.