This paper outlines the results of an investigation into the adsorption of trimethylgallium (TMGa) on GaAs(100) surfaces at 300 K and its subsequent thermal chemistry carried out using Auger electron spectroscopy, temperature programmed desorption methods and reflection-absorption IR spectroscopy (RAIRS). The data are compared to previously obtained data for triethylgallium adsorption at these surfaces and discussed in terms of reactions that lead to carbon deposition and the relative reactivities of As-rich and Ga-rich surfaces. Very preliminary RAIR data for TMGa adsorption at the Ga-rich surface reveal that some surface reaction does indeed occur at 300 K but that at least some of the methyl groups appear to remain intact. Thermal decomposition of the species formed by TMGa adsorption is found to be highly sensitive to experimental conditions and generally results in high levels of residual carbon, in marked contrast to the behaviour of TEGa.This paper outlines the results of an investigation into the adsorption of trimethylgallium (TMGa) on GaAs(100) surfaces at 300 K and its subsequent thermal chemistry carried out using Auger electron spectroscopy, temperature programmed desorption methods and reflection-absorption IR spectroscopy (RAIRS). The data are compared to previously obtained data for triethylgallium adsorption at these surfaces and discussed in terms of reactions that lead to carbon deposition and the relative reactivities of As-rich and Ga-rich surfaces. Very preliminary RAIR data for TMGa adsorption at the Ga-rich surface reveal that some surface reaction does indeed occur at 300 K but that at least some of the methyl groups appear to remain intact. Thermal decomposition of the species formed by TMGa adsorption is found to be highly sensitive to experimental conditions and generally results in high levels of residual carbon, in marked contrast to the behaviour of TEGa.