The increasing demand for long-distance high voltage direct current (HVDC) technology requires the adaptation of gas-insulated systems or lines, which were originally developed for the alternating current (AC) grid. These products are particularly relevant to massively reduce required volume and footprint compared to air-insulated solutions, e.g. in city in-feed or HVDC offshore platforms. Robust dimensioning of DC gas-insulated systems requires the knowledge of the electrical field distribution at all times. Starting from a capacitive distribution at voltage switch-on, the field distribution evolves towards a resistive distribution at a pace dictated mainly by the conductivity of the solid epoxy insulation. The spatial distribution of the epoxy conductivity is in turn very sensitive to the temperature distribution in the system. In gas-insulated systems, gas and solid insulations are electrically in parallel. As a consequence, if dielectric failure occurs in most cases in the gas near surfaces, it is often mediated by space charges in or on the solid. Space charge accumulation near the surface, – i.e. the net surface charge – is the result from a competition between charging currents from the solid, respectively from the gas side. It is therefore also crucial to quantify and model the contribution from gaseous ionic conduction. There, besides natural ionization from cosmic and terrestrial radiation, additional voltage-dependent ionic sources may be present: Electronic emission and collision ionization near rough electrode surfaces, protrusions, particles, or triple-junctions. This contribution presents an experimental validation scheme for modeled DC electrical field distribution. It is based on (i) me asurements of electrical curre nts in the solid and the gas, (ii) measurement of surface potential distribution of the surface of epoxy insulators, and (iii) determination of flashover voltage of insulators under HVDC stress. To mimic the effect of ohmic losses in the conductor, a temperature gradient is applied across the insulator. DC Field distributions are calculated with a finite element model taking into account the relevant charge transport processes in the gas as well as in the solid. Additionally, transient fields are also predicted, e.g. during the transition from an initial capacitive distribution to the final resistive distribution, or after polarity reversal or impulses superimposed on DC fields.