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For homo-junction Si bipolar transistor (Si BJT) operation under common emitter, because of self-heating and the positive feedback of thermoelectricity, thermal runaway occurs easily at high collector-emitter voltage and high current, this decreases the safe operation area (SOA) of transistors. In this paper, due to negative feedback of thermoelectricity, the negative differential resistance (NDR) characteristics of Si/SiGe/Si double heterojunction bipolar transistors (DHBTs), with heavily doped base, at high currents, are observed. A new interpretation of this phenomenon is given. This may result from Auger recombination in the base and a decrease in current gain at high current as temperature rises by self-heating effects. As a result, this phenomenon has benefits to improve the anti-burnout capability of bipolar transistors. The results indicate power Si/SiGe/Si HBTs have a self-regulating ability and confirm that they are suitable for high power applications.