The present invention relates to a method of inspecting a product, comprising extracting defects from the product, classifying the defects on the basis of information about the extracted defects representing the analogy of the defects, extracting the feature data of the defects on the basis of the result of defect classification, and feeding back the feature data of the extracted defects for inspection; and to an inspection system comprising an inspecting means for extracting defects from the product, a defect classifying means for classifying the defects on the basis of information about the defects extracted by the inspecting means representing the analogy of the defects, and a feature data extracting means for extracting the feature data of the defects on the basis of the result of defect classification provided by the defect classifying means, characterized in that the feature data of the defects extracted by the feature data extracting means is fed back to the inspecting means for inspecting the product. The present invention relates also to a method of manufacturing a semiconductor device or the like, comprising extracting defects from the semiconductor device or the like, classifying the defects on the basis of information about the extracted defects representing the analogy of the defects, extracting the feature data of the defects on the basis of the result of defect classification, and feeding back the feature data of the extracted defects to an apparatus for manufacturing the semiconductor device or the like.