50 nm period gratings were produced on thick GaAs substrates by using electron beam lithography and two‐step wet chemical etching. The size was very close to the theoretical limit of the electron beam lithography. For transferring such a fine grating onto GaAs, a two‐step wet chemical etching method was developed, where a H2SO4‐H2O2‐H2O system is first used to roughly etch the oxygen and carbon‐contaminated GaAs surface, followed by surface planarization with a Br‐CH3OH system.