Does linearity of a N-MOSFET continue for Vds below 0V?

[expert_vision]

I operate a N-MOSFET (2N7000) in a simulator in the linear region very close to Vds=0. In fact Vds is between -50nV and +50nV.

In the simulator the output seems to be linear, but is this in reality happening? What happens if Vds goes a few tens of nV below 0V ?

Vgs=5V constant (on state)

 

[FvM]

The linear behaviour is real, present both in device equations and empirical behaviour. For most MOSFETs with source shorted to substrate, it ends when the drain-substrate diode starts to conduct.