AbstractThis paper describes three types of high voltage power transistors that are in widespread use in the electronics industry today, and their susceptibility to reverse‐biased second breakdown while switching unclamped inductive loads. It provides a brief explanation of the phenomenon of second breakdown in transistors under both forward‐biased and reverse‐biased conditions. It describes a stress circuit that has been developed to incorporate switching of unclamped inductive loads as an integral part of operational life testing. A case history incorporating this technique is presented for the 2SD1739 high voltageNPNbipolar power trans