A P-substrate MOSFET (often called PMOS) is a MOSFET with opposite doping types (N instead of P and P instead of N in the cross-section in figure 1). This MOSFET is made using a P-type substrate, with a P− epitaxy. As the channel sits in a N-region, this transistor is turned on by a negative gate to source voltage. This makes it desirable in a buck converter, where one of the terminals of the switch is connected to the high side of the input voltage: with a N-MOSFET, this configuration requires to apply to the gate a voltage equal to formula_7, whereas no voltage over formula_8 is required with a P-MOSFET.