High quality rapid thermal annealing of InP and GaAs at elevated temperatures was achieved in a load‐locked rapid‐thermal‐low‐pressure‐metalorganic‐chemical‐vapor deposition (RT‐LPMOCVD) reactor, under phosphorus and arsenic controlled ambient, using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBA) organometallic liquid sources. Damage‐free surfaces of InP and GaAs were obtained for temperatures up to 700 °C for InP under TBP ambient, or above 900 °C for GaAs under TBA ambient, respectively. Annealing the III–V substrates at low protective ambient pressure (50 mTorr) provided an excellent surface protection through the heating cycle without resulting in deposition of the group‐V elements on the surface and without reducing the efficiency of the process.