Thin WO3 and Y2O3 films were successfully prepared on Si substrate by the cold gas dynamic spray process (CGDS, or cold spray). In contrast to standard metallic coatings such as Al, Cu on soft metal substrate, there was no sizable crater formation and plastic deformation of ceramic powders (WO3, Y2O3) on Si substrate. However, the aggregation of raw powders were found to be fragmented on the substrate to form a highly irregular surface with very fine secondary particles and provide a good interlocking powder among particles in the coating. High-resolution images of the substrate interface showed that particles at the interface were well packed and good adhesion was obtained. Therefore, the particle bombardment onto the first layer of the coating could provide enhanced adhesion to the substrate mechanically and/or chemically. (C) 2003 Elsevier B.V. All rights reserved.