PURPOSE: To ensure high speed operation and to achieve cost reduction and operational stability by preliminarily incorporating a detector in a semiconductor device and measuring the input timing of data by a low speed tester.

CONSTITUTION: A data signal input terminal 1 is successively connected to the inverters 6, 7, 8, 9 of a delay circuit 3 and the output from the circuit 3 is connected to the signal input terminal of a data holding circuit 4. When the devices constituting the circuit 3 are almost uniformly arranged, the high speed operation of a semiconductor device can be judged from the positive correlation of high speed operation and a delay time. By inputting the output of the circuit 3 to the circuit 4, the judgment of delay can be performed only by adjusting input timing and it is unnecessary to judge the output of the circuit 4 within a real time and, further, the input timing of data can be measured by a low speed tester. By preliminarily incorporating a detector in the semiconductor device and using the low speed tester, high speed operation can be ensured and cost reduction and operational stability can be achieved.