A heterojunction bipolar transistor (HBT) is provided with an improved on-state breakdown voltage V.sub.CE. The improvement of the on-state breakdown voltage for the HBT improves the output power characteristics of the HBT and the ability of the HBT to withstand large impedance mismatch (large VSWR). The improvement in the on-state breakdown voltage is related to the suppression of high electric fields adjacent a junction of a collector layer and a sub-collector layer forming a collector region of the HBT.