High quality GaAsSb/InP double heterojunction bipolar transistor (DHBT) structures were grown using gas-source molecular beam epitaxy. The substrate temperature and V/III flux ratio were optimized to grow single phase GaAsSb base layers lattice matched to InP. The do gain as high as 40 was obtained in 60 x 60 mu m(2) GaAsSb/InP DHBTs with a 500 angstrom carbon doped (7 x 10(19) cm(-3)) GaAsSb base layer. High performance DHBT with a 250 angstrom base layer shows a current gain cutoff frequency f(T) of 346 GHz and maximum oscillation frequency f(max) of 145 GHz. (c) 2006 American Vacuum Society.