The gas-phase chemistry and reactions between trimethyl gallium ((CH3)(3))Ga, TMGa) and ammonia (NH3) were investigated by the use of quantum chemical calculations employing density functional theory techniques. Reactive intermediates and reaction pathways originating from the initial formation of the gas-phase adduct between TMGa and NH3 were identified. The lowest activation Gibbs free energy for the formation of methane For these reactions involving the TMGa:NH, adduct is 34 kcal/mol. In addition, a further reaction intermediate was identified having the stoichiometry TMGa:(CH3)(2)GaNH2 :NH3, and this intermediate eliminates methane with a low Gibbs free energy activation barrier of 20 kcal:mol. Therefore, it appears that the production of methane from TMGa and NH, may be an autocatalytic process. The implications for reactor design and growth are discussed.