A study of the decomposition of chemically activated trimethylsilane and methylethylsilane is reported. Chemical activation was by the insertion of singlet methylene, from the photolysis of diazomethane at 3660 Å and 24°, into the C-H and Si-H bonds of dimethylsilane. The total rate constants for trimethylsilane, kTMS, and methylethylsilane, kMES, unimolecular decomposition were found to be 2.93 × 107 sec-1 and 3.30 × 107 sec-1, respectively. H2, CH4, and C2H6 were formed as decomposition products in the presence of the radical scavengers, oxygen and 1,3-butadiene, indicating they are formed by molecular elimination processes. The experimental results combined with RRKM calculations infer that Si-C bond rupture and methane elimination are the major primary decomposition paths for chemically activated trimethylsilane, and Si-C bond rupture and molecular hydrogen elimination are the major primary decomposition paths for chemically activated methylethylsilane. The rate constant for methyl rupture from the chemically activated trimethylsilane, 2.2 ± 0.8 × 107 sec-1, yields an A factor for Si-C bond rupture in trimethylsilane, via RRKM theoretical calculations, equal to 1015.6 ± 0.6 sec-1.