Etching characteristics of GaAs, InP, and other materials using a scanning microplasma have been investigated. This technique utilizes enhanced reaction between a reactive ambient gas and a target at an excited region like a microplasma which is produced by irradiating a scanning focused ion beam. It was observed that the present technique gives an enhanced etching rate over a physical sputter etching and a very smooth etched surface. Dependence of etching rate on bombarding angle and reactant gas flow rate is also measured.