PURPOSE: To protect a hybrid IC while preventing excessive protection by a method wherein heat sensitive semiconductor elements are fixed to a resistor provided on a conductor in series with an output circuit to detect a temperature rise of the resistor interrupting the output circuit current.

CONSTITUTION: The transistors 1, 2 are fixed on a copper foiled conductor 12 of an insulated Al plate 11 through the intermediary of a heat sink 13 connecting an emitter to the conductor 12. A plated resistor 3 not exceeding 0.2Ω is provided on the conductor 12 in series fixing to an Si planar type transistor 4. The transistor 4 detects the voltage fluctuation due to a temperature change of the element 4 interrupting the current of the elements 1,2. In the concrete, a relay 6 is inserted into the power supply line between the element 2 and the driver step thereof driving the relay 6 by means of a detecting output 5. In such a constitution, the transistors 1, 2 are not actuated by excessive current incoming from an instantaneous high signal input preventing excessive protection with accurate temperature detection and high reliability due to the detection by the resistor 3.