Carbon-doped InP/InGaAs single heterojunction bipolar transistors (SHBTs) and double heterojunction bipolar transistors (DHBTs) have been grown by solid-source molecular-beam epitaxy using CBr4 as p-type dopant precursor. DC characteristics of InP/InGaAs composite collector DHBT have been compared with the SHBT. A Current gain of 40 and breakdown voltage of 10 V were obtained for the composite collector DHBT with no obvious knee-shaped characteristics or switching effect. The results show the composite collector design of DHBTs can effectively suppress the current blocking effect and improve the breakdown voltage. Furthermore, this study elucidates the complex breakdown mechanisms in the composite collector DHBTs. (C) 2004 American Vacuum Society.