A method of correcting an optical proximity effect may include the steps of: fabricating a test mask having test patterns; projecting patterns on a wafer using the test mask; measuring line widths of the patterns formed on the wafer; and executing a model calibration using the measured line widths and writing a correction recipe. The entire area of the wafer chip may be divided into a plurality of templates. An optical proximity correction may be executed on one of the templates and it may be verified that the optical proximity correction was executed properly on another template. The data for the templates that pass a verification may be merged and final data may be written using the merged data. A photomask may be fabricated using the final data.