The circuit presented by Cor Van Rij for characterizing JFETs is a clever solution. Noteworthy is the use of a five-pin test socket wired to accommodate all of the possible JFET pinout arrangements.
The RJF0604JPD Thermal FET switch has the over temperature shut-down capability sensing to the junction temperature. This FET has the built-in over temperature shut-down circuit in the gate area. And ...