The lifetime of power transistors significantly depends on the junction temperature swings. These temperature swings occur when the load conditions change. A closed loop junction temperature control system is designed to increase the lifetime of power transistors. The control system reduces the occurring temperature swings by influencing the power loss of the power transistor. This is done by adjusting the gate driver's supply voltage, which affects the switching speed and the conduction characteristics. The junction temperature is measured by determination of the temperature sensitive internal gate resistor via the high-frequency-gate-signal-injection method and fed back to the controller.