The chips with defects, which escape the test, will cause the quality problem and will hurt the goodwill and decline the revenue. It is important to look for the defect root causes and to derive the prevention strategy. In this paper, a case study of a 64 M-DRAM is used to demonstrate the approaches of failure analysis in silicon debug stage and, consequently, the determination of the tests for the production. The consideration of test derivation is both to enhance the yield and to improve the product quality with low-test cost. The root causing, electrical modeling of defects, test selection and guardband determination will be introduced. Finally, a quantitative measure is given to show the value of failure analysis for a high volume DRAM product.