The characteristics of impulse corona have been studied in a point‐to‐plane gap. Both positive and negative square voltage pulses of one‐ and two‐microsecond duration were used with various voltages and pulse repetition rates. The impulse corona in air is found to be quite similar to the d.c. corona, except that the phenomena are exaggerated by the relative absence of space charge inhibition. At higher voltages, the negative impulse corona was found to have a ``spike'' or streamer type of discharge superimposed on the regular Trichel pulse corona. By using the nonelectron‐attaching gases nitrogen and hydrogen, it is shown that these spikes are due to the negative ion space charge formed by the Trichel pulse in the gap. When the point is grounded, the intense field developed between this negative space charge and the positive space charge at the point is sufficient to cause a streamer to propagate.