ZnO varistor is like back-to-back diodes which is bipolar. Since it behaves like a diode, it has a breakdown voltage ranging from several volts to thousands of volts. However, the biggest highlight of ZnO varistor is the high voltage (and high current) stability up to kV and kA ranges where most diodes/electronics explode. Therefore, it finds applications in high-voltage protection against power surges and transients.