How to calculate MOSFET internal gate resistance?
A simplified way to model/look at the gate of an NMOS can be this:







simulate this circuit &ndash; Schematic created using CircuitLab

There will be a series resistance Rs

There will be a parallel resistance Rp

There will be the gate capacitance Cgate

Although not so clear from your question I think you are asking about Rs, the series resistance.

Asking about Rp would not make much sense anyway as it is often too high to even measure. Some manufacturers specify a gate input current and then Rp should be a current source in the model or even better (more accurate), a diode with a leakage current. This diode is sometimes present for ESD protection but it often leaks more than the gate itself!

But back to Rs, this Rs depends on the shape and material used to make the gate structure inside the MOSFET. There is no way for you as an end user to know what size, shape and material (and it's resistance) the gate is made off. Semiconductor companies regard this as their "trade secret".

Luckily, for almost all of the normal applications of these MOSFETS, you generally do not need to know the value of Rs as it will almost always be low enough. My guess is that for most power MOSFETs the value of Rs will be a few ohms at most.

The only applications I see where the value of Rs does matter is for extremely fast switching. Fortunately the fastest switching speed or largest delay is often mentioned in the datasheet.

I have seen other cases where the gate resistance was indeed relevant but that was for an on-chip CMOS filter. There the value of Rs was calculated by the MOSFET models so I could optimize my MOSFETs to minimize Rs. But that's on-chip low power design, this has little to do with power MOSFETs for switching applications.