Heavily Beryllium doped (~1.5 ×10 19 cm -3 ) InP/InGaAs single heterojunction bipolar transistors (SHBTs) and double heterojunction bipolar transistors (DHBTs) have been successfully grown by solid source molecular beam epitaxy (SSMBE). The epitaxial growth was performed on a VG 90H MBE system with 100mm wafer growth capability. The novelty of this process was the use of dimeric phosphorus generated from a gallium phosphide (GaP) decomposition source which permitted growth at fairly low temperature (420 o C) while conserving extremely high quality materials. Thermal stability studies were then performed on the heavily doped HBTs using postgrowth annealing in an N2 ambient. The devices were annealed over a temperature range of 350-550 o C for 15 minutes prior to fabrication. The relatively low growth temperature of ~420 o C and the use of stoichiometric conditions for both the arsenides and phosphide materials produced remarkably thermally stable, high-gain SHBTs and DHBTs up to annealing temperatures of 550 o
