PURPOSE: To prevent electrostatic breakdown by a method wherein surge voltage is absorbed to each other by forming a transistor element connected in one island region to external terminals and a transistor element as the protection element.

CONSTITUTION: An N-P-N transistor element 2 used as the input transistor of a differential amplification circuit is provided in a semiconductor substrate 1, and the base and the collector of the transistor 2 are connected to external lead terminals 4 via pads 3, respectively. A P type base region is formed in the island region where the transistor 2 has been formed, so as not to change the bias condition to the emitter of the element 2, further, an N-P-N transistor element 5 as the protection element is provided by forming an N type emitter region in this base region, and the emitter region of the element 5 as the protection element is connected to the base region of the element 2. This can prevent electrostatic breakdown without influence on normal circuit action.