The heterojunction barrier effects（HBE） in Si/SiGe/Si double heterojunction bipolar transistors （DHBTs） at various temperatures are studied.It is found that HBE becomes more evident with the increase of the valence-band discontinuity △Ev at the BC heterojunction.For a given △Ev at the BC heterojunction

as the temperature is reduced

HBE becomes more remarkable and seriously degrades HBT performance parameters.Based on above results

the effective measures to alleviate the HBE are proposed.These results will be very important for the design and development of low-temperature-operation microwave power SiGe HBT.