1. A rule-based OPC evaluating method comprising the steps of: obtaining correction data by correcting design data about an evaluation-use mask pattern through rule-based OPC; forming said evaluation-use mask pattern into an evaluation-use mask based on said correction data; forming evaluation-use gate patterns into an evaluation-use wafer using said evaluation-use mask; obtaining measured data about said evaluation-use gate patterns by measuring lengths of said evaluation-use gate patterns formed on said evaluation-use wafer; creating a simulation-based OPC model through execution of process calibration based both on test pattern design data about a test-use mask for process calibration purposes, and on measured data about gate patterns of a test-use wafer fabricated using said test-use mask; obtaining simulation data by simulating said design data about said evaluation-use mask pattern using said simulation-based OPC model; and evaluating said rule-based OPC by comparing said measured data about said evaluation-use gate patterns with said simulation data.