Is pinch off voltage of JFET constant?
If you look at the situation where you hold Vgs constant and then increase Vds:  Vds appears as a voltage drop along the channel, increasing as you move from source to drain.  Therefore the reverse bias voltage between gate and channel also varies with length and is highest at the drain end.  The channel acquires a tapered shape and the Id --> Vds relationship becomes non-linear.  At high enough Vds the channel pinches off and you get saturation.

The pinch off conditions are dependant upon not just Vgs but also Vds.

This is from the physics of the situation.

What I am not sure of is if Vp is defined for a set of conditions.


if that is the case Vp MAY not vary even though you get pinch off as very different Vgs levels depending upon Vds.

but that would be because it is a defined level.

once defined you should be able to use it in all situations

unless the transport mechanism changes -> ballistic transport.



-> note I'm not certain about this last part.