SiC:Hˆlms have been deposited by reactive rf magnetron sputtering of Si target in helium and methane (diluted by argon) gas mixtures. The eŠects of helium partial pressure ratio R on the structural, optical and electrical properties of theˆlms were investigated. With increasing R above 75, both the optical bandgap and the concentration of hydrogen bonded to silicon atoms decreas, and the dark conductivity increases rapidly. These data imply that the nanocrystallization of SiC:Hˆlms could be attained by introducing hellium in the sputtering process.