Provided are a thermistor with 3 terminals, a thermistor-transistor including the thermistor, a circuit for controlling heat of a power transistor using the thermistor-transistor, and a power system including the circuit. The circuit includes: a thermistor-transistor which comprises a thermistor having a resistance decreasing with an increase in temperature and a control transistor connected to the thermistor; and at least one power transistor which is connected to a driving device to control a supply of power to the driving device, wherein the thermistor-transistor is adhered to one of a surface and a heat-emitting part of the at least one power transistor and is connected to one of a base, a gate, a collector, and a drain of the at least one power transistor to decrease or block a current flowing in the at least one power transistor when the temperature of the at least one power transistor rises, so as to prevent the power transistor from heating up.