In a first embodiment, an ultra-fast breakover 
diode has a 
turn on time TON that is less than 0.3 microseconds, where the forward breakover 
voltage is greater than +400 volts and varies less than one percent per ten degrees Celsius change. In a second embodiment, a breakover 
diode has a reverse 
breakdown voltage that is greater, in 
absolute magnitude, than the forward breakover 
voltage, where the forward breakover 
voltage is greater than +400 volts. In a third embodiment, a string of series-connected breakover 
diode dice is provided, along with a 
resistor string, in a packaged circuit. The packaged circuit acts like a single breakover diode having a large forward breakover voltage and a comparably large reverse 
breakdown voltage, even though the packaged circuit includes no discrete 
high voltage reverse breakdown diode. The packaged circuit is 
usable to supply a triggering current to a 
thyristor in a voltage protection circuit.