A planar dielectric barrier discharge device has been tested for exhaust emission reduction in simulated engine exhaust. This device's electrical characteristics have been measured and are presented in this paper. The device consists of two dielectric barriers which act like series capacitors, with the gas gap between them. At low gap voltages, the gas gap also acts like a capacitance, with a much smaller capacitance than the barriers. At higher voltages, the gas gap breaks down and a blue–purple glow visually fills the gap. The partially ionized gas conducts charge across the gap, building electrical charge on the dielectric barrier inner surface. When the AC excitation voltage peaks and starts to go toward an opposite polarity, the discharge momentarily extinguishes, trapping charge in the dielectric barrier capacitance. As the applied voltage continues toward the opposite polarity peak the gap voltage again exceeds the threshold voltage and the discharge resumes, transferring charge back across the gas gap.Several means are available to estimate the barrier and gap capacitances. Using data for total device current and voltage having adequate resolution and accuracy, it is possible to calculate the current through and the voltage across the plasma. Thus, it is possible to calculate the current–voltage (I–V) characteristic of the ionized gas in the gap. Voltage and current sampling circuit considerations are discussed; it is critical to have low–noise signals but this can be accomplished easily with readily available measurement equipment.Such measurements are reported for a range of electrode geometries and temperatures. Results show good agreement with the simple equivalent circuit model.