A protection device is provided that is placed in series connection between an input or signal node and a node to be protected. If the node to be protected is a relatively high impedance node, such as the gate of a MOSFET, then the protection device need not carry much current. This enables it to be built to be very fast. This enables it to respond rapidly to an overvoltage event so as to protect the circuit connected to the node to be protected. The protection device may be used in conjunction with other protection cells that offer greater current carrying capability and controllable trigger voltages, but which are intrinsically slower acting.