Hydrogenated germanium‐carbon alloy (GeC:H) films have been deposited by a reactive rf magnetron sputtering of Ge in methane–argon gas mixtures. As the second sputtering gas, helium is utilized in order to control the film properties. The effect of helium partial pressure ratio R to the total sputtering gas on the structural, optical and electrical properties of the films was investigated. The films show the amorphous nature in the low‐R range up to 60%. In the high‐R range above 60%, the bonding configuration in IR spectra changes, the diffraction lines of XRD appear, the optical bandgap decreases, and the dc conductivity increases clearly. It is found from these data that the microcrystallization of GeC:H films could be achieved by introducing helium during the sputtering process. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)