The thermodynamic and photochemical stability of Ga2O3–GaAs interfaces fabricated usinginsitumultiple‐chamber molecular beam epitaxy has been investigated. The Ga2O3films were deposited on clean, atomically ordered (100) GaAs surfaces using a molecular beam of gallium oxide. Thermally induced degradation of electronic interface properties such as interface recombination velocityS(5750±1250 cm/s) and interface state densityDit(mid‐1010cm−2 eV−1range) has not been observed after rapid thermal annealing at 800 °C. Furthermore, no interface degradation has been detected during exposure to high intensity laser light. The preservation of excellent electronic interface properties and the absence of interfacial chemical reactions are attributed to AsxOyand elemental As free Ga2O3–GaAs interfaces. ©1996 American Institute of Physics.