I have simulated high side N channel enhancement MOSFET (BSC12DN20NNS3) circuit which has Vth of 3.6V.

according to the theory , when gate voltage is greater than 53.6V , MOSFET turns on and when gate voltage is below 53.6V , MOSFET should be in cut off and acts as open switch .

but in simulation and reality,source terminal is constant at Vg-Vth (20V-3.6V=16.4V) irrespective of drain voltage.

what could be the reason of constant source voltage (Vg-Vth) even though MOSFET is in cutoff ? is it leakage current that causing voltage drop at source terminal ?

[![enter image description here](https://i.stack.imgur.com/YOIFN.png)](https://i.stack.imgur.com/YOIFN.png)