The low pressure pyrolysis of alkylmetals on resistively heated substrates was studied using multiphoton and electron ionization mass analysis. The activation energy for the production of gas phase methyl radicals from the decomposition of trimethylgallium under single collision conditions was found to be 26 ± 3 kcal/mol, which is to be compared to 13 ± 2 kcal/mol previously observed for trimethylaluminum. No evidence could be found for any surface radical reactions leading to the production of CH4 or C2H6. A proposed deposition mechanism accounting for these observations was tested by pyrolyzing trimethylgallium in the presence of hydrazine. No change in methyl signal was observed, supporting the theory that radical reactions do not occur on the surface under the conditions employed.