The thermal decomposition of Ga(CH3)(3) has been studied both experimentally in shock-heated gases and theoretically within an ab-initio framework. Experiments for pressures ranging from 0.3 to 4 bar were performed in a shock tube equipped with atomic resonance absorption spectroscopy (ARAS) for Ga atoms at 403.3 nm. Time-resolved measurements of Ga atom concentrations were conducted behind incident waves as well as behind reflected shock waves at temperatures between 1210 and 1630 K. The temporal variation in Ga-atom concentration was described by a reaction mechanism involving the successive abstraction of methyl radicals from Ga(CH3)(3) (R1), Ga(CH3)(2) (R2), and GaCH3 (R3), respectively, where the last reaction is the rate-limiting step leading to Ga-atom formation. The rate constant of this reaction (R3) was deduced from a simulation of the measured Ga-atom concentration profiles using thermochemical data from ab-initio calculations for the reactions R1 and R2 as input. The Rice-Ramsperger-Kassel-Marcus (RRKM) method including variational transition state theory was applied for reaction R3 assuming a loose transition state. Structural parameters and vibrational frequencies of the reactant and transition state required for the RRKM calculations were obtained from first-principles simulations. The energy barrier E-3(0) of reaction R3, which is the most sensitive parameter in the calculation, was adjusted until the RRKM rate constant matched the experimental one and was found to be E-3(0) = 288 kJ/mol. This value is in a good agreement with the corresponding ab-initio value of 266 kJ/mol. The rate constant of reaction R3 was found to be k(3)/(cm(3) mol(-1) s(-1)) = 2.34 x 10(11) exp[-23330(K/T)].