High voltage CMOS switch with protection against diffusion to well reverse junction breakdown

A high voltage CMOS n-well switch with guarding against reverse junction breakdown, as well as gate-aided breakdown. The CMOS switch of the present invention comprises two pairs of cascoding p-channel MOSFET loads, two pairs of cascoding n-channel MOSFET drivers and an inverter for input. One device in each pair of MOSFETs is used as a guard against gate-aided breakdown. The p-channel MOSFETs have independent n-wells so that the guard devices have their n-wells independently biased without being pulled by the n-wells of the load devices. The inverter is used to provide complementary inputs to the switch. By having independent n-wells, the breakdown voltage of the switch is raised above p+/n-well reverse breakdown voltage.