(001) GaAs surfaces treated with ultrasonic‐running de‐ionized water (U‐RDIW) after NH4OH/H2O2/H2O etching are investigated by reflection high‐energy electron diffraction (RHEED) and by x‐ray photoelectron spectroscopy (XPS). RHEED observations show a spotty (1×1) pattern lying on the 0‐th Laue circle at room temperature, a (2×4) streaky pattern at 310 °C, and a spotty (3×6) pattern after annealing at 370 °C. We discuss the difference in surface stoichiometry after U‐RDIW between the H2SO4‐ and NH4OH‐etched surfaces based on the results of XPS. The experimental results indicate the possibility of controlling the surface stoichiometry of the U‐RDIW‐treated GaAs surfaces by varying the etching solution.