Abstract: In response to the processing needs of photoelectrochemical mechanical polishing of the third-generation semiconductor material gallium nitride (GaN), an optoelectronic chemical mechanical polishing (PECMP) device with ultraviolet light irradiation, voltage loading and mechanical polishing functions was developed. The polishing disc unit with ultraviolet light directly shining on the surface of the GaN wafer, and the electrical circuit with stable loading voltage in the processing area and insulated from the device was designed. The driving mechanism was designed which has independent rotation of polishing disc and workpiece disc, reciprocating movement of polishing disc and adjustable loading of polishing pressure. The three-dimensional model of the whole PECMP device was established, and the structure of key components such as polishing disc and gantry was optimized through static analysis and modal analysis. The PECMP polishing device was built and the performance test was carried out. In the test, the applied light intensity was 0~200 mW·cm⁻², the voltage size was 0~10±0.1 V, the insulation resistance was 150 MΩ, the polishing disc speed was 10~100 r/min, the workpiece speed was 10~200 r/min, the polishing disc reciprocating moving speed was 1~100 mm/s, and the pressure loading range was 0~200 N, which met the PECMP processing needs of 2-inch GaN wafers.