Hydrogen (H) plasma irradiation effect on (100)  GaAs surfaces was studied. The etching of GaAs surfaces was found to be effectively ceased after some etch at the initial stage when the plasma beam was incident on the surface at a shallow glancing angle. The etched surface was an atomically flat (100)  GaAs surface as previously observed by clear Laue spots in the reflection high‐energy electron diffraction measurement reported by I. Suemune, Y. Kunitsugu, Y. Kan, and M. Yamanishi [Appl. Phys. Lett.55, 760 (1989)]. A physical model for the newly found relation between the etch rate and the surface structure is discussed.