An integrated circuit wherein a gate circuit is provided on a bus line mounted on a semiconductor substrate. The gate circuit is used to separate an unused circuit block from other circuit blocks which are connected to a bus line through an input-output circuit for high speed data transmission, thereby reducing a parasitic capacity which might be imparted to the bus line by the separated circuit block. The input-output circuit is formed of a clocked inverter. The gate circuit is formed of a C.multidot.MOS transmission gate. The input-output circuit and gate circuit are so connected that where the gate of the inverter is opened, then the C.multidot.MOS transmission gate is closed; and where the gate of the inverter is closed, then the C.multidot.MOS transmission gate is opened.