CdS films, 200 nm thick, for photoconductive sensor applications were prepared at various H-2/(Ar+H-2) flow ratios on glass substrates at room temperature by radio-frequency magnetron sputtering. The sulfur concentration in CdS films crystallized at room temperature with (002) preferred orientation depends directly on the hydrogen atmosphere; the surface roughness of the films gradually increases with increasing hydrogen atmosphere. Films deposited at 8% of H-2/(Ar+H-2) exhibit an abrupt decrease of dark- and photoresistance, showing a low photosensitivity (R-dark/R-photo). Films deposited at a hydrogen atmosphere of 42% exhibit a photosensitivity of 5x10(3), maintaining a photoresistance of an approximately 2x10(4) Omega/square. The dark- and photoresistance values of CdS films were related by a composition, surface roughness, and defect sites within the bandgap. (C) 2008 The Electrochemical Society.