The silane plasma used in the preparation of amorphous silicon based devices by the radio frequency plasma enhanced chemical vapour deposition (rf-PECVD) method may be conveniently characterised with the help of the optical emission spectroscopy (OES). In the present paper we have studied the rf glow discharge plasma of a flowing mixture of silane and argon formed between the capacitor plates of a rf-PECVD chamber by the OES method. Our aim is to find a correlation between the intensity of the emission spectra arising due to the excitation of silane, and the process parameters. The intensity variation of the peak at 414.3 nm arising due to SiH (A2 δ — X2II) transition has been studied with respect to different process parameters like the flow ratio of sinale to argon, applied rf power density and pressure. The theoretical calculations of the evolution of the concentration of SiH* species satisfactorily conform to the intensity variation of the emission spectra of this species. This method makes possible an in-situ control of the quality of the material or device by monitoring the plasma in a non-intrusive way.