Thermodynamic equilibrium calculations for the systems n-methoxysilane, SiH4-n(OCH3)(n), n = 1-4, were performed using the STANJAN computer code. The required enthalpy and entropy data for the methoxysilanes were estimated using the MOPAC computer program for semi-empirical molecular orbital calculations. The calculated solid-phase compositions were not sensitive to +/- 10% changes in the n-methoxysilane enthalpy and entropy values. For n = 2, 3 or 4, the equilibrium solids were comprised of SiO2 and C. The purest SiO2 was predicted for 2-MEOS at atmospheric pressure, low temperature, and an excess of hydrogen. For all n-methoxysilanes, the solid carbon content increased rapidly at moderate temperatures but did not continue to increase at the highest temperatures.