A CO2 gas discharge laser includes elongated planar live and ground electrodes vertically spaced and electrically insulated from each. The electrodes are spaced apart by ceramic spacer strips arranged along the edges of the electrodes. An auxiliary electrode is located at each end of the live electrode, co-planar with the live electrode, longitudinally spaced part from the live electrode vertically spaced apart from, but electrically connected to, the ground electrode. The auxiliary electrode has two raised portions spaced apart by a distance less than the distance between inside edges of the ceramic strips. The raised portions of the auxiliary electrode prevent erosion of the ceramic strips by laser radiation generated in the resonator when the laser is operating.