The possibility of gas-phase conversion of tetramethoxysilane to trimethoxysilane was thermodynamically and experimentally evaluated. Tetramethoxysilane is a byproduct of a proposed process for production of poly-crystalline silicon from trimethoxysilane without using chlorine compounds. It was found that a trimethoxysilane yield of more than one percent is possible under conditions of 0.1 MPa and 1023 K with a Si-Cu catalyst.