The invention relates to a semiconductor device comprising a bipolar transistor having a collector (1), a base (2) and an emitter (3) at its active area (A). The semiconductor body (10) of the device is covered with an insulating layer (20). At least a part of a base connection conductor (5) and an emitter connection conductor (6) extend over the insulating layer (20) and lead to a base connection area (8) and an emitter connection area (9), respectively. The known transistor is characterized by poor gain, particularly at high frequencies and at high power. A device according to the invention is characterized in that the emitter connection area (8) and the base connection area (9), viewed in projection, are present on the same side of the active area (A), the emitter connection conductor (6) is divided into two or more sub-conductors (6A, 6B) and the base connection conductor (5) is divided into one or more further sub-conductors (5) which are present between the sub-conductors (6A, 6B) and form a co-planar transmission line (T) therewith. In this way, the inductance of the emitter connection conductor (6) is reduced considerably, resulting in a much higher gain, particularly at high frequencies and high power. Preferably, the semiconductor body (A) is interrupted at the area of the transmission line (T) and is glued to an insulating substrate (40).