In order to find out the mirror-finish conditions for GaAs with non-damage, which is used for semiconducting devices in ultra high frequencies with very high speeds, a disc type chemical polishing machine being made trially, improvement in flatness is pursued from viewpoints of the machine motion and of the properties of polishers and the surfaces produced by Br2--methanol solution are estimated. The results obtained are as follows : (1) Macrogeometric asperities are not removed by chemical polish in dipping, regardless of the disappearance in microgeometric roughness. (2) Flatness is no more than several microns with a cloth polsher, though roughness of about 0.01 μ is obtained. (3) Flatness is improved up to about 1 μ with mirror finish, when used a cloth phenolic laminated sheet made polisher having V-grooved checkers patterns on its surface. (4) Scratchings axe exposed, and etch pits are produced on {111} face, unless the concentration of the solution is reduced to 0.0025%.