Lead sulfide (PbS) nanoparticle films were chemically grown on glass, quartz and silicon substrates. Structure and size of PbS nanoparticles were characterized by X-ray diffraction and transmission electron microscopy (TEM), respectively. Large optical band gap has been observed in these films. The decreases in dc-conductivity, Hall mobility and carrier concentration with reducing grain size were also examined. Heterojunctions of p-PbS/n-Si were fabricated and photovoltaic effect was observed in these self-assembled heterojunctions. (C) 2003 Elsevier B.V. All rights reserved.