A composite power semiconductor is disclosed which is adapted to avoid second breakdown and therefore provide stable operation. The composite semiconductor consists of an array of parallelconnected integrated circuits constructed in a single chip, each circuit comprising an output power device, for connection between an electric power source and a load, and one or more associated low-level control amplifiers. The effect of the thermal instability called second breakdown in such an array is to channel a disproportionate amount of electric current through the output device undergoing second breakdown, thereby increasing the temperature of the affected output device, thereby increasing the current, etc. until failure occurs. In the power semiconductor disclosed, the output power device and associated low-level amplifier are thermally closely coupled so that each is at all times substantially at the temperature of the other or bears a predetermined temperature relationship therewith, and the two are interconnected in a fashion that will produce high electrical gain. There is negative thermal feedback so that a change in power dissipation with resulting temperature change in the output device causes the low-level amplifier to alter the electric current carried by the output device. For example, an increase in temperature which will tend to cause the output device to conduct a larger amount of electric current and which will also tend to cause the low-level amplifier to conduct a larger amount of current, can have the result, because of the close thermal coupling and interconnection, of maintaining the output current substantially constant.