This thesis presents a novel diagnosis technique for multiple defects. This technique proposes a simple heuristic to partition the failures log so that hard-to-detect defects and easy-to-detect defects are likely to be separated. Hopefully, each defect can be diagnosed individually. This technique requires only commercial diagnosis software with a simple add-on tool. No customized diagnosis software is needed. Simulations on benchmark circuits demonstrated the effectiveness of the proposed technique. Real silicon experiments on a real industrial product have been verified by physical failure analysis.