Diffuse discharges were studied in an impedance‐matched experimental system. A traveling‐wave transmission line system was used to produce a high‐voltage pulse (up to 40 kV), with a rise time of approximately 2 ns and a total pulse width of approximately 100 ns. Gas mixtures of C3F8 and c‐C4F8 with He in a pressure range between 100 and 600 Torr were investigated. Plane parallel electrodes with 10‐cm diameter and electrode spacings from 0.25 to 1.5 cm provided uniform field conditions in the discharge region. UV radiation produced by a flashboard placed behind a perforated anode surface provided the volumetric preionization necessary for maintenance of the diffuse discharge. A low ionization potential seedant was used to assure a uniform preionization. High‐current‐density diffuse discharges were maintained for approximately 100 ns. At low‐current density, the diffuse discharge in an electronegative gas mixture operated under balanced electron growth conditions with constant voltage. At high‐current densities (above 100 A/cm2), the discharge operating voltage decreased and was found to be as much as two times lower than the low‐current glow‐discharge voltage. The operating voltage also decreased with time during individual discharge under such conditions.