GaAsSb is a low band gap, lattice matched to InP, alternative to GaInAs. Growth and doping using diethyltellurium and carbon tetrachloride were investigated. Hole concentrations up to 1.3×1020 cm -3 have been achieved in as-grown carbon-doped GaAsSb [i.e., no postgrowth annealing was necessary for dopant activation, a key requirement for n-p-n heterojunction bipolar transistor (HBT) structures]. This is a sevenfold improvement over the best carbon-doped InGaAs reported by metalorganic chemical vapor deposition. Hall measurements indicate that GaAsSb's hole mobility is 55%-60% of GaInAs's, for a given carrier concentration. InP HBTs with carbon-doped GaAsSb base are demonstrated.