A p-type semiconductor, bulky AgGaS2, was prepared by the conventional solid state reaction and heat-treated at various temperatures under He and H2S gas flow to eliminate vacancies or interstitial defects and to improve the crystallinity. A p-n diode, n-CdS/P-AgGaS2 was fabricated by decorating AgGaS2 surface with nanoparticles of n-type US by the hydrothermal treatment. The configuration was confirmed by XRD, UV-vis spectroscopy and TEM. The composite photocatalyst of this new configuration exhibited a high rate of hydrogen production under visible light irradiation (lambda >= 420 nm) from water containing sulfide and sulfite as hole scavengers. The photocatalytic diode system formed with n- and p-type semiconductors results in efficient charge separation, caused by the rectification of photo-electrons and holes generated upon photo-absorption. (c) 2006 Elsevier B.V. All rights reserved.