A semiconductor integrated circuit is segmented into a plurality of blocks. Each block includes a switching transistor which is connected between the CMOS circuit of the block and the ground point and is adapted to shut off the current of the CMOS circuit by being controlled by a test mode control signal, and a leakage current detecting circuit which has a self-check function for the block. A signal which is the logical sum of the outputs of the leakage current detecting circuits of all blocks is led out of the semiconductor integrated circuit through a common external output terminal.