The characteristics of a double heterojunction bipolar transistor(DHBT) depend closely on the type of band alignment structure at the hetero-interface between emitter-base(E-B) heterojunction and base-collector(B-C) heterojunction. Based on thermionic-field-diffusion model, the comparisons are made of the DC and the RF characteristics between two novel HBTs, that is, InAlAs/GaSbAs/InP DHBT and InP/GaSbAs/InP DHBT, of which the former has a type-I E-B junction and a type-II B-C junction and the later has a type-II E-B junction and a type-II B-C junction. The simulation results show that DHBT with a type-I E-B junction and a type-II B-C junction has much better current driving capability, DC gain and RF performance, although it has a slightly high turn-on voltage.