Barrier shallow donor states have been investigated in Si-doped GaAs/AlGaAs quantum well structures by means of magneto-photoconductive spectroscopy. In order to promote formation of barrier-only donors, only barrier regions have been doped in the present work. High resolution and signal-to-noise ratio barrier donor spectra have been obtained, which clearly demonstrate the advantage of the photoconduction measurement technique. Observation of barrier donor transitions in a single quantum well structure is also reported. Good agreement is found between experimentally and theoretically determined magnetic field dependence of donor transition energies. (C) 2004 American Vacuum Society.