We report the improved thermal stability of heavily C‐doped GaAs layers using atomic layer chemical beam epitaxy (ALCBE). The use of ALCBE improves the crystal quality and reduces hydrogen incorporation in the epilayers by about a factor of 2, resulting in enhanced electrical dopant activity as compared to conventional growth techniques. This process has been successfully applied to the fabrication of InGaP/GaAs heterojunction bipolar transistors (HBTs) with a highly C‐doped base grown by ALCBE and other layers grown by conventional CBE. Dc current gains up to 150, for a base doping layer of 3×1019cm−3, have been obtained. Moreover, the thermal stability of these devices is increased, as indicated by a post‐growth annealing (650°C, 60 min) which induces only a slight current gain degradation of about 20% at high collector currents, to be compared to a degradation of 60% for HBTs conventionally grown by CBE.