Why use a PMOS transistor instead of a diode for ESD protection?
The purpose of the diode and MOSFET are for reverse polarity protection, not ESD. The diode is more simplistic, but it is lossy as it will drop some voltage across it (0.4&nbsp;V to 1.0&nbsp;V, depending on the type). The p-channel MOSFET should have a much lower voltage drop if chosen properly.