Next up for testing is the FQP7N20, a much lower power TO220 as compared to the last package, which was a TO247. It exhibits much sharper current discontinuity as VGS passes the threshold voltage than the IRFP150MPBF did.

It looks like using a single mosfet is not the correct way to make a dc load, I may need something a bit more complicated. The mosfets are likely not operating in the triode region since VDS is too high in this case (10V).