Thin-film solar cells from polycrystalline silicon on inexpensive nonsemiconductor substrates are an option for reducing costs. We have investigated the deposition of silicon layers on ceramic substrates. The aim was to manufacture high-quality polycrystalline silicon films with a thicknesses lip to 40 mu m. The experiments focused on nucleation and growth of silicon on ceramics. Our research has shown that the deposition of a silicon layer on ceramic substrates cannot be compared with the well-known growth mechanism of silicon on amorphous substrates like SiO2. As examples we have chosen two ceramic materials differently structured: polycrystalline Al2O3 and SiALON, which is characterized by a strong vitreous phase. The nucleation of silicon is influenced by the chemical composition and by the microstructure of the ceramic material. The crystalline structure of the additionally growing silicon layer depends on the nucleation phase. With this in mind, it is possible to influence the crystalline structure of the silicon layer. The maximum grain size of a 40 mu m thick silicon layer can be increased from 3 mu m on SiAlON up to 30 mu m on Al2O3 substrates.