A mixture of Si2H6and C2H2was used for deposition of SiC by ArF‐excimer‐laser chemical vapor deposition. Optical emission spectroscopy was employed to study the radicals CH, C2, SiH, and Si atoms in the photolyzed gas. The line intensities were measured changing the disilane/acetylene flow ratio. The concentrations of excited CH and C2were very low without disilane, however they rapidly increased with the addition of disilane. This is attributed to the reactions of silicon‐based radicals with C2H2or C2H to form CH and C2. A measurement on the deposition rates of the films agreed well with the result.