Microcrystalline Si 1-xGe x (x-0.8) films have been deposited by RF magnetron sputtering with source frequency of 100MHz. Crystallinity of deposited films has been evaluated by spectroscopic ellipsometry. Detailed investigation on the deposition behavior has been carried out, and it was found out that threshold temperature for crystalline phase formation is about 300°C. At the substrate temperature of 300°C crystallinity depends on film thickness, i.e. as film becomes thicker, crystallinity increases from less than 5% to about 60%. On the other hand, at substrate temperature of 350°C, crystalline formation begins to take place almost from the beginning of deposition. Nucleation site density is lower for 300°C, which in turn results in the higher surface crystallinity compared with the films deposited at 350°C. Substrate bias effect on deposition behavior was also investigated. Substrate bias improves the crystallinity of the films deposited at 300°C while it actually damages crystalline phase formed at 350°C.