What is the purpose of connecting Zener diodes between a MOSFET gate and its source or drain?

MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) feature a gate that is electrically isolated from the channel by an extremely thin layer of silicon dioxide. While this provides a very high input impedance, it also makes the device highly vulnerable to high-voltage transients, particularly static electricity. If a static charge or voltage spike exceeds the dielectric strength of this thin oxide layer, it will puncture the insulation and permanently destroy the transistor. To prevent this, Zener diodes are often integrated or connected between the gate and the source or drain. These diodes act as voltage clamps; if a static spike hits the gate, the Zener diode will reach its breakdown voltage and harmlessly shunt the excess energy away, protecting the fragile oxide layer from static damage.