We report a method for formation of a ridge with almost vertical sidewalls in the fabrication of ridge stripe AlGaInP laser diode structures, which cannot be easily achieved when a conventional wet-etch process is used, for high power operation with a fundamental transverse mode. By depositing additional oxides protecting layers on the sidewalls after the dry-etch process, a wet-etch process, which is necessary to remove the plasma-induced damaged portion of the etched region, can be safely applied and the vertical ridge shape maintained. Using this method, the ideally rectangular ridges were obtained and the single mode operation of. 660 nm laser diode with up to 270 mW output power was successfully achieved. (c) 2005 American Vacuum Society.