Abstract: The photoelectro-chemical etching system of compound semi-conductor is disclosed. The system comprises a laser generator, a shutter to cut off laser beam, a laser beam chopper, a secondary high reflection mirror, a beam expander, a waveform generator, a chopper controller, a potentiostat to apply the reverse or forward voltage to the optical glass cell. Instead of applying the reverse-bias voltage to a semiconductor material, the reverse and/or forward voltage with a uniform pulse period is applied so that homogeneous and damage-free surface is obtained and etching process is made available in a more efficient manner.