To maintain product reliability and robustness, current generation submicron integrated circuits need to pass high quality and exhaustive testing programs before being shipped off to the customer or released into the market. Precise and reliable silicon debug is essential to the semiconductor industry. It identifies problems caused by design changes, process anomalies and rarely used applications. This is essential to drive the corrective action at the earliest stage of production. This paper describes the systematic approach of a complex design debug in one of the ASIC device.