Compact gas-insulated metal-enclosed systems for HVDC applications (HVDC GIS) have been developed for HVDC projects in need of space-saving installations, such as offshore platforms, cable transition stations or multi-terminal switching stations. HVDC GIS are on the market up to rated DC voltages of ±550 kV. Within the German offshore grid connection system DolWin6, the world’s first offshore HVDC GIS was successfully installed and tested during commissioning in the dockyard in year 2021. High-voltage testing was carried out with AC voltage stress and partial discharge measurement according to recommendations within CIGRE technical brochure 842. As a special part of the commissioning, also a high-voltage test using DC voltage was performed. All commissioning tests of the offshore HVDC GIS ±320 kV were passed successfully.