It is easy to melt the semiconductor in a semiconductor device long before the solder or package materials are melted. Above a certain temperature threshold, t

It is easy to melt the semiconductor in a semiconductor device long before the solder or package materials are melted. Above a certain temperature threshold, the electrical resistance of semiconductors drops exponentially with temperature, which is why NTC (negative thermal coefficient) thermistors are made of semiconductor materials. This causes a positive feedback loop that increases the current very quickly and concentrates it through a narrow channel through the semiconductor (so the current density can be extremely high even when the total current is still low), which can easily reach 1500 Celsius degrees, melting the silicon, while the temperature of the package and of the solder remains very low (because the time is too short for the temperature to propagate outwards from the melted silicon channel).