Nanosecond pulsed powers produce streamer discharges which are suitable for chemical reactions. The discharges in wire-plate electrodes and wire-cylinder electrodes are observed. The dense area where streamers exist should be utilized as a high-performance reactor. Widely distributed streamer discharges were observed. On the other hand, spark discharges, which would decrease in reactor performance, were observed when shorter gap separation was adopted. © 2006 IEEE.