AbstractThe homogeneous gas‐phase decomposition kinetics of methylsilane and methylsilane‐d3have been investigated by the comparative‐rate‐single‐pulse shock‐tube technique at total pressures of 4700 torr in the 1125–1250 K temperature range. Three primary processes occur: CH3SiH3→ CH3SiH + H2(1), CH3SiH3→ CH4+ SiH2(2), and CH3SiH3→ CH2= SiH2+ H2(3). The high‐pressure rate constants for the primary processes in CH3SiH3obtained by RRKM calculations are log (k1+k3) (s−1) = 15.2 ‐ 64,780 Cal/θ and logk2(s−) = 14.50 ‐ 67,600 → 2800 Cal/θ. For CH3SiD3these same rate constants are logk1(s−) = 14.99 ‐ 64,700 cal/θ logk2(s−) = 14.68 – 66,700 → 200