Aqueous colloidal systems of composite silver metal and CdS semiconductor of different size were investigated. Coating the CdS colloids with silver islands leads to composite structures with electronic properties differing considerably to the sum of the separate particles. Evidence for the deposition of the silver on CdS is obtained from optical spectroscopy and High Resolution Transmission Electronic Microscopy. (C) 2004 Elsevier B.V. All rights reserved.