The thermal rate constants and H/D kinetic isotope effects (KIEs) of the reactions SiH4 + H SiH3 + H2 and SiH4 + CH3 SiH3 + CH4 were calculated with the variational transition state theory including multidimensional tunneling corrections (VTST-MT). The ωB97X-D and CCSD(T) methods were employed to compute the barrier height and reaction energy. The ωB97X-D/aug-cc-pVTZ methodology was used to build reaction paths, and the CCSD(T)/CBSQ-5 approach was used to improve the energetics of the stationary points in the calculations of CVT/μOMT thermal rate constants. For the SiH4 + H pathway, the CVT/μOMT rate constants and H/D KIEs are in excellent agreement with previous experimental and theoretical calculations; otherwise, for the SiH4 + CH3 pathway, which has few experimental and theoretical data available, it has provided, for the first time, rate constants and kinetic isotope effects using variational transition state theory with multidimensional tunneling corrections.