Ion layer gas reaction (ILGAR), a novel thin-film technology for sulfides is introduced. Its peculiarity is the low-temperature conversion of a solid metal salt precursor into a sulfide compound by reaction with gaseous H2S. The capability of this technique is demonstrated by the preparation of CdS, which is either of cubic or hexagonal polycrystalline structure. Spectralphotometric measurements reveal a high optical band gap of 2.78 eV. A subsequent annealing process reduces this value to 2.45 eV. This fact as well as XRD results indicate a nanocrystalline structure of the ILGAR-deposited CdS thin films. (C) 2001 Elsevier Science B.V. All rights reserved.