Q. Explain the construction of depletion MOSFET?

A slab of p-type material is formed from a silicon base and it is referred to as the substrate. It is the foundation upon which the device is constructed.  In some cases substrate is internally connected to the source terminal. The source and the drain terminals are connected through metallic contacts to n-doped regions linked by an n-channel. The gate is also connected to a metal contact surface but remains insulated from the n-channel by a very thin SiO2 layer. So there is no direct electrical connection between the gate terminal and the channel of a MOSFET. Insulating layer of SiO2 also accounts for the very desirable high input impedance of the device.