Polycrystalline silicon carbide (poly-SiC) films were deposited on SiO2 and Si3N4 substrates at temperatures between 1050 degreesC and 1280 degreesC by APCVD and characterized using SEM and TEM. In general, the average grain size of the as-deposited films on both substrate types increases with increasing deposition temperature. Poly-SiC films deposited on Si3N4 have a dense microstructure and small grain size, whereas poly-SiC deposited on SiO2 have a large grain size, and a low density interface region which contain voids. The observed differences in the deposited films may be due to a high energy barrier for poly-SiC deposited on SiO2.