In this work a heat generation model induced by current crowding is proposed. This model, in turn, is applied to the thermal calculation of typical multi-finger emitter structures of BJTs. The internal temperature distribution obtained from this model provides clear indication of the existence of hot spots in base-emitter contact region. The characteristics of the location and the magnitude of hot spots are also presented in this paper. Various pertinent effects due to the non-uniform heat dissipation are discussed. The result of this study serves to locate potential hot spots, which must be considered to prevent thermal breakdown of power BJTs as well as other types of power devices.