The surface decomposition of trisdimethylaminoarsenic (TDMAAs) on GaAs (001) has been studied employing supersonic molecular beam scattering. It was found that TDMAAs molecules adsorbed dissociatively on GaAs (001) surfaces at room temperature through a Langmuir adsorption mechanism. The initial Ga-rich(4×6)surface changed into an As-richc(4×4)surface after the injection of TDMAAs. The species such as dimethylamine and methylmethyleneimine desorbed at the surface temperatures of 150 and 230 °C, respectively, as measured by temperature-programmed desorption (TPD) spectra. The polar-angle dependence of desorption showed that the desorption of species has two maximal intensities, at the directions along surface normal and 60°, respectively. ©1997 American Institute of Physics.