MEASUREMENT OF JUNCTION TEMPERATURE OF AN ALGAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTOR OPERATING AT LARGE POWER DENSITIES/

An electrical method to determine the junction temperature of a power bipolar transistor is presented. The success of this method does not r ely on the constancy of thermal resistance over the wide range of oper ating temperatures. It is hence suitable for transistors operating at high power densities where conventional measurement techniques would n ot apply. Using this method, we establish that the junction temperatur e can be 40 degrees C higher than the product of tile low temperature thermal resistance and the power dissipation.