Growth of epitaxial (Al,Ga)As/Al/(AlGa)As by molecular beam epitaxy was not found successful. Thermal expansion coefficient mismatch between Al and GaAs and reduction of Al melting point by partial dissolution of incident Ga and As species and with species diffusing across the metal‐semiconductor interface, make epitaxial (AlGa)As growth on Al above ∼300 °C impossible. Below ∼200 °C GaAs tends to be polycrystalline. Even below 480 °C GaAs becomes semi‐insulating by high deep level concentrations.