The growth of GaAs by molecular-beam epitaxy using trimethylgallium (TMGa) or metal gallium, and trisdimethylaminoarsine (TDMAAs) was investigated in relation to carbon incorporation into the epitaxial layers and the growth rate. In the case using TMGa, the high concentration of residual carbon (2 10 1 9 cm - 3 ) in GaAs grown at 490°C rapidly decreased along with an increase in the TDMAAs flux intensity, eventually reaching (1-2) 10 1 6 cm - 3 . The growth rate of GaAs grown by using metal Ga or TMGa, decreased along with increasing TDMAAs flux intensity. These results indicate that the species derived from TDMAAs adsorbed on the growing surface and strongly influenced the adsorption/desorption of Ga adatoms as well as TMGa.