A method of correcting optical proximity effect of contact holes. Corresponding relations between mask critical dimensions (mCDs) and photoresist critical dimensions (pCDs) for each pitch (d) are formed. Correction of each mCD for each combination of pCDs and pitches is determined based on the corresponding relations. The correction is used first to correct each contact hole of a processing mask pattern. The first corrected contact hole of the processing mask pattern is corrected again to a square having the same area as the first corrected contact hole and the same center as the uncorrected contact hole.