We present an emitter design capable of reducing the current crowding effect in high power heterojunction bipolar transistors. An Esaki diode, vertically integrated to the transistor, limits the maximal emitter current density. The current crowding reduction is observed using effective base resistance measurements. Advantages in protecting high power transistors against thermal instabilities are discussed and the increased safe operation range is demonstrated. (C) 2002 Elsevier Science Ltd. All rights reserved.