The high‐energy Auger spectra were measured for a large number of molecular‐beam epitaxial (Al, Ga)As layers, and analyzed for Al composition using electron microprobe and reflection electron diffraction oscillations for calibration. A simple analysis employs this calibration and avoids assumptions of column III/V stoichiometry. Thus the bulk composition can be established to within a few percent from the Auger peak heights, in spite of a large variation in the As surface coverage. An effort is made to account for differences between Auger sensitivity factors determined for as‐grown surfaces (this study) and those obtained from measurements performed during Ar+ion sputtering. Our measurements support recent measurements of the band gap of AlxGa1−xAs which place the direct/indirect crossover composition betweenx=0.37 and 0.39.