Electrochemical deposition of PbSe nanocrystals onto p-Si(100) was studied in dark and under illumination. The underpotential deposition of lead on selenium was used for PbSe electrosynthesis. It was shown that electrocrystallization of PbSe in dark conditions can proceed only at the presence of lead nanoparticles (Pb-0) on Si surface. The particles were formed using two methods: either cathodic deposition of metal or silicon oxidation by Pb2+ ions in solution. Photoelectrochemical deposition of PbSe on p-Si (100) substrates proceeds without the preliminary stage of Pb-0 formation. Si/PbSe heterostructures formed both in dark and under illumination were characterized by cyclic voltammetry, SEM, EDX, AFM and XRD. (C) 2005 Elsevier B.V. All rights reserved.