Is it possible to physically destroy a microcontroller with software?
Of course you can, with the HCF instruction!

That said, I say that's impossible without any external circuitry, apart from power and such.

Even including some non purposely faulty connections possibly won't cut it: if you tie all the gpios to a power rail, setting them as output (to the opposite power rail) that can dissipate quite a lot of power. A gpio pin is probably protected against short circuit and such so nothing harmful will happen.

Designing an external circuit that destroys the chip at will is not trivial too in my opinion. The first thing that comes to mind needs a somewhat high voltage power supply, a nmos and a resistor:







simulate this circuit &ndash; Schematic created using CircuitLab
Where:


\$V_{CC}\$ is the usual supply for the micro, some 3v3 to 5V or whatever is needed
HV is a supply which voltage is well above the absolute maximum ratings of the micro
D1 is there to protect your valuable 3V3 voltage source
R1 pulls the mosfet gate high when the micro is not keeping it to ground
M1 is the designated killer


the operation is simple: if the micro releases GPIOx M1 turns on, Vcc rises and your chip catches fire. Note that this is a crappy setup, for example HV must be turned on after you are extra sure that GPIOx is firmly held to ground. Some transistors might not like some -5V Vgs, and so on... But you get the picture.