Normally, in MOSFET datasheet, it provides Ciss, Coss and Crss vs Vds with Vgs @ 0V.
I cannot recall I see this plot with Vgs change from negative to positive at a certain Vds condition.
How that textbook suggest the MOSFET should be tested to get that curve. But from the description, it test a p-type substrate MOS… Here I am testing a VDMOS n-channel model by modifying my template which can test those parameters. (How to make tests circuits for typical characteristics for a mosfet? - QSPICE - Qorvo Tech Forum)
