An experimental study of the photolysis of trimethylsilane-diazomethane- oxygen mixtures and tetramethylsilane-trimethylsilane-diazomethane-oxygen mixtures at 4358 and 3660 Å is reported. Experimental rate constantsf or the decomposition of chemically activated ethyl trimethylsilane, ethyldimethylsilane, and tetramethylsilane are determined. These specific rates range from 3×104 sec-1 to 6.5×105 sec-1. A comparison of the 4358- and 3660-Å rate constants for tetramethylsilane decomposition with RRKM theory calculations suggest that a thermal A factor of 1015.0±0.5 sec-1 is correct for primary decomposition by Si-C bond rupture. The uncertainty in this A factor reflects the uncertainties in the E* and E0 values for chemically activated tetramethylsilane. A discussion of this A factor relative to that found previously for neopentane decomposition is given.