A method of manufacturing a mask includes designing a second mask data pattern for forming a first mask data pattern, creating a first emulation pattern, which is determined from the second mask data pattern, using a first emulation, creating a second emulation pattern, which is determined from the first emulation pattern, using a second emulation, comparing a pattern, in which the first and second emulation patterns overlap, with the first mask data pattern, and manufacturing a mask layer, which corresponds to the second mask data pattern, according to results of the comparison.