Multiple-quantum-well Ga1-xAlxAs-GaAs heterostructures grown by metalorganic chemical vapor deposition have been analyzed by Auger electron spectroscopy combined with simultaneous argon-ion sputter etching. The chemical-interface widths of the Ga0.45Al 0.55As-GaAs heterojunctions are determined to be ≲17 Å. In addition, no Al is detected in the GaAs quantum wells.