A bipolar transistor having a base electrode of an air bridge structure is simplified in structure and enhanced in the degree of freedom of a contact position of a base wiring line with the base electrode. The bipolar transistor has a semiconductor mesa portion having a base layer formed on an upper face thereof, and a base electrode contacts with the base layer and has a floating extension which extends from the semiconductor mesa portion to a space on the outer side with respect to the semiconductor mesa portion. The floating extension is used as a contact portion for a base wiring line to the base electrode.