We investigated dependence of GaAs(0 0 1) surface roughness and etching rate on thermal-cleaning temperatures (400-600 degrees C) and beam pressures of TDMAAs (4 x 10(-6)-1 x 10(-4) Torr) in order to obtain the optimum cleaning condition. It was found that a very smooth surface with roughness less than 0.2 nm was obtained in spite of a large etching rate (similar to 70 nm/h) when the thermal-cleaning temperature and the beam pressure were 525 degrees C and about 8 x 10(-5) Torr, respectively. In addition, TDMAAs irradiation was very effective to smoothen a rough GaAs(0 0 1) surface.