By measuring the steady‐state potential distribution inn—GaAs samples with ohmic contacts, very high electric fields have been found near the anode contacts. In samples withn · L(carrier concentration × sample length) products greater than 1012cm‐2, switching from the Gunn mode to a high current, lower (constant) voltage state takes place along with the appearance of a high field at the anode. In samples withn · Lproducts less than 1012cm‐2the buildup of the high field is accompanied by a sudden increase in current. These high currents are due to carrier generation in a narrow region near the anode.