PURPOSE: To detect whether voltage to be applied is certainly applied to the interior of a semiconductor, by providing a circuit, which utilizes the rising of power supply voltage to be applied to discriminate the application of predetermined voltage, in a semiconductor device.

CONSTITUTION: An LSI 21 is successively mounted on the socket of an ageing substrate 1 and said substrate 1 is inserted in an ageing apparatus to apply predetermined ageing voltage of 5V. Voltage is changed from 0V to 5V at the power supply terminal 22 of the LSI 21 according to the timing sequence shown by a drawing (b) and this change is detected by the power-only-set circuit 23 of the LSI 21 and the output thereof is set to an LOW level. The LOW output of the circuit 23 is reversed by an inverter 24 and an HIGH level is led out to a monitor terminal 25. Therefore, after the substrate 1 is inserted in the ageing apparatus, the potential at the terminal 25 of the LSI 21 is measured to apply predetermined voltage and it can be easily discriminated whether ageing is performed.