Dry-etch damage, introduced by a low biased 92-MHz anode-coupled reactive ion etching (RIE), in MBE-grown undoped GaAs has been characterized by photoreflectance (PR) and photoluminescence (PL) measurements. PL spectra show emission peaks at 1.516 eV (excitons) and at 1.494 eV (D-A, B-A) before etching, whereas a new emission peak at around 1.488–1.490 eV appears after the RIE. The depth distribution of this new emission center, examined by PL measurements with a combination of step wet etching, has a Gaussian-shape with a l/e value of 56 nm. A very small number of nonradiative recombination centers are considered to be generated, because the integrated PL intensity including both emission peaks at 1.490 eV and at 1.516 eV is the same before and after the RIE. The surface recombination rate of the sidewall formed by the RIE is almost the same as that of the wet-etched surface. This low-damage etching has been applied to fabricate ultra-fine GaAs patterns to provide a nanometer-scale ridge structure with a cross-section 15-nm wide by 150-nm high. The low damage etching condition is also suitable for precise fabrication.