How is "Overtemperature shutdown/protection" implemented for ICs?
In short: a comparator-with-hysteresis compares a fixed voltage with a temperature-dependent voltage and shuts down the series transistor while it trips.


A fixed-voltage source is fundamental part of any voltage regulator.
A temperature-dependent voltage source can be as simple as a diode. The challenge for IC designers is to make the temperature-independent voltage source!
a comparator with hysteresis is a fundamental circuit: positive feedback is the key.