Abstract：Junction-case thermal resistance has always been a highly concerned thermal parameter of power

semiconductor devices，which is also the standard to weight the heat sink performance of power semiconductor

devices. Heat-sink design should be considered in order to prevent device overheating damage. Therefore，accurate

measurement of thermal resistance is particularly important for system heat-sink. The difficulty of devices thermal

resistance measurement lies in the junction temperature measurement because it is difficult to measure junction

temperature directly without destroying the devices package. Found through experiment that when the conduction

voltage under small constant-current was used as the temperature-sensitive parameter，the conduction voltage and

temperature had good linearity，which can be used for junction temperature measurement. Finally，the thermal

resistance measurement can be completed based on the thermal resistance formula when the junction temperature

was known.

      Key words：GaN devices；conduction voltage；junction temperature；thermal resistance