The structural, optical, electrical, and optoelectronic properties of magnetron sputtered hydrogenated amorphous‐silicon carbon alloy films have been investigated as a function of sputtering pressure. The optical band gap, the activation energy of dark conductivity, and concentration of hydrogen increase with increasing sputtering pressure. The photoconductivity as well as the dark conductivity shows a maximum against pressure. These results are discussed from the standpoint of the structural and compositional change of the films with sputtering pressure, originating from the change of plasma reaction process composed of the decomposition of methane and the sputtering of silicon.