Performance degradation due to fatigue accumulation from the repetitive switching of high load current is critical to understanding robust power MOSFET product design. In this paper, we present a novel high-current-temperature (HCT) characterization system used to investigate real world powercycling failure mechanisms. The effects of electric current Joule heating, non-uniform temperature distribution and performance deterioration of discrete power devices are discussed. Thermal fatigue of solder joints and thick aluminum wire bonding are common weak spots with regard to power-cycling capability. We report performance failure mechanisms and discuss the superposition of contributing factors in defining root cause. Results discuss various package influences as part of a robust power MOSFET development process.