Ultra-thin Nb2O5 films with excellent uniformity have been grown on Si (1 0 0) by atomic-layer-deposition using Nb(OC2H5)(5) and H2O precursors, and the corresponding thermal stability has been studied through atomic force microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The results indicate that the ultra-thin (similar to 3 nm) Nb2O5 film is gradually built up into distributed large islands with increasing rapid thermal annealing (RTA) temperature. Meanwhile, both crystalline and amorphous phases are formed in the matrix of Nb2O5 annealed at 700 degrees C. In terms of the as-prepared sample, an interfacial layer (IL) with a thickness of around 1.5nm is observed, that is composed of niobium silicate (Nb-O-Si). Further, the high temperature RTA leads to a thickened IL, which is attributed to the formation of more Nb-O-Si bonds and new silicon oxide (Si-O-Si) adjacent to the Si (1 0 0). (C) 2011 Elsevier B.V. All rights reserved.