A semiconductor wafer critical dimension measurement method comprising receiving an image of a site of the semiconductor wafer comprising a plurality of features, processing the image to measure at least one critical dimension of at least some of the features, analyzing the critical dimension of each feature and determining the feature to be a non-defective feature or a defective feature, and using the critical dimension of at least some of any non-defective features as a measure of the critical dimension of features of the semiconductor wafer.