Power MOSFET transistors are voltage controlled switches. They begin to turn on at their rated “gate threshold voltage” or Vgs(th). Most of the datasheet ratings are given for a fully saturated condition, typically 10 volts. There is also a maximum allowable gate voltage, Vgs, that is typically 20 volts. Any voltage greater than that will pierce the thin metal oxide layer that insulates the gate from the rest of the silicon die, destroying the device. This is why uninstalled MOSFETS can be so sensitive to electrostatic discharge (ESD) damage.