Abstract: There is disclosed a spike suppressor which is capable of switching very high currents at very high speeds. Typically, a current in the order of 80 amperes can be switched in less than 1 nanosecond. The device is also capable of dissipating high power. Typically, 80-ampere, 200-nanosecond pulses at a repetition rate of 10 per second can be tolerated. The device consists of a relatively thick layer (greater than 1 micron) of a refractory transition metal oxide such as NbO.sub.2 grown on a conducting refractory substrate. The metal oxide is polycrystalline and can be grown in several different ways.