A novel embedded sensing and diagnosis method is proposed for early detection of on-state resistance (Ron) variations in power transistors. It is intended for the reliability improvement of power electronics systems. The proposed technique is based on the sensing of drain-source voltage, and used for the monitoring of component aging or early warning of component failure. The measured VDS is processed by a filtering behavioral model which eliminates high-level noise perturbations coming from the supply rail and provides a reliable early awareness of Ron degradation.