The increasing demand to transport electrical energy over vast distances makes the usage of high voltage direct current (HVDC) links increasingly economic. Due to the compact design, the independence from environmental conditions and the high reliability, the focus is shifting to gas-insulated DC systems (DC-GIS). Particularly because of the capacitiveresistive transition and the charge carrier accumulation under DC-voltage stress on each gas-solid interface it is necessary to develop dimensioning and testing guidelines for DC-GIS. Partial discharges in the gas insulation under DC voltage stress become more critical due to the high amount of generated charge carriers. The charge carriers can accumulate on the gas-solid interfaces between the solid spacers or the interface of dielectric coated electrodes and the insulating gas SF6. The accumulation of charge carriers on the surface of coated electrodes can lead to surface discharges on the interface. The presented experimental and numerical results show that the coating used for DC-GIS needs to have a higher electrical conductivity as the one currently used for AC-applications in order to avoid this surface discharges.