Measurements of the actual power and silane consumption as a function of excitation voltage and pressure in a completely characterized radio-frequency, glow-discharge chamber used for the deposition of a-Si:H, are reported. The influence of these parameters on the discharge power and impedance is presented and discussed with consideration of the basic electron heating and power dissipation mechanisms. The discharge is more efficient, in terms of the amount of energy spent per dissociated silane molecule, at higher pressures and lower voltages. This amount tends toward the dissociation threshold of silane for lower power densities. The rate constant of electron impact dissociation of silane, calculated from silane consumption, increases with power with a different trend for each pressure, and is higher for lower pressures ranging from 0.08 to 0.2 s(-1).