Nearly stoichiometric, amorphous silicon carbide films with a relatively low hydrogen content were deposited from organsilanes on a variety of substrates in a microwave-generated plasma without external heating. The films undergo little weight loss upon pyrolysis to 800-degrees-C. The effect of the different deposition parameters on the film composition and the exhaust gas was established through a battery of tests including infrared Fourier transform spectroscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy, ellipsometry, and mass spectroscopy. For a given power level there is a limiting feeding rate of the precursor under which operation of the system is dominated by thermodynamics and thus leads to the desired product. Beyond that limit, excessive hydrogen incorporation and carbosilane polymer formation takes place. The hydrogen content of the plasma is also an important parameter affecting the chemistry of the deposition. In the thermodynamically dominated regime the nature of the precursor has no effect on the quality of the film. It affects only the relative utilization efficiency.