This letter presents the scanning tunneling microscopy (STM) images of GaAs(001) surfaces prepared by deoxygenated and de‐ionized water (DODIW) treatment. The STM images reveal that the missing‐dimer rows and unit cells of the 2×4 structure and atomic‐layer steps of Ga–As clearly appear after heating the samples above 500 °C in an ultrahigh vacuum. These experimental results suggest the DODIW treatment can attain atomically flat GaAs(001) surface. ©1995 American Institute of Physics.