A method of creating data of a mask for manufacturing a semiconductor device. The mask includes at least one auxiliary pattern arranged adjacent to a line pattern. The at least one auxiliary pattern is allocated in accordance with a rule-based method on the basis of an interval between a first line pattern and a second line pattern adjacent to the first line pattern. Size of the at least one auxiliary pattern is then optimized in accordance with a model-based OPC (Optical Proximity Correction), by shifting edges of the at least one auxiliary pattern and edges for one of the line patterns on the basis of a first light intensity threshold on the at least one auxiliary pattern and a second light intensity threshold on the line patterns.