What is the Proper Voltage to Open a 350v Rated Power N Channel Mosfet?

[Crazymechanic]

A simple and quick question please clear this up.
Let's say I have a 350v rated power n channel mosfet , how much of positive voltage do i have to apply to the gate to fully open the mosfet?

I know this varies from type of transistor and so but the average?
i am just getting mixed up some things like the voltage drop let's say i need to apply 20 volts does that mean that on the Drain there will be my let's say 300v dc and then on the gate i should apply like 290 or something or i just should apply 20volts.
I guess I am saying is the gate voltage measured from the drain reference or from zero volts reference?

Thanks.

 

[Enthalpy]

The gate voltage is measured versus the source.

How much depends on each transistor and is given by the datasheet; 15V gate-to-source is a common value, and destruction at 30V an other common value.