The hydrogenation of silicon deposited on a substrate for photovoltaic applications has been obtained by a plasma torch. This method shows a great advantage and leads to the improvement of the electronic properties of the material. The hydrogenation of silicon allows the crystallographic defects elimination (dislocations, dangling bonds) which leads to an increase of the diffusion length. In order to understand silicon hydrogenation by RF inductive thermal plasma spraying, a study of the discharge by optical emission spectroscopy (OES) has been undertaken. This study has been compared with the hydrogen content measured by the exodiffusion technique. The detection of highly excited species of atomic and molecular hydrogen proves the specificity of the inductive plasma. Hydrogen emission lines have been used to calculate the electronic density on the plasma axis, Furthermore, the ArI lines were used to calculate the electronic temperature in the plasma. With this information, the deviation from the local thermodynamic equilibrium (LTE) of the plasma has also been estimated. (C) 2002 Elsevier Science B.V. All rights reserved.