SEMICONDUCTOR DEVICE WITH A HIGH-FREQUENCY BIPOLAR TRANSISTOR ON AN INSULATING SUBSTRATE

A bipolar transistor (3) is provided with a first main surface (4) in contact with a conductive mounting surface (2), and with an opposed second main surface (12) having connection pads (5, 6, 40) for an emitter, base, and collector. The lateral dimensions of the conductive mounting surface (2) are practically equal to the dimensions of the first main surface (4) of the transistor (3), and may thus be relatively small. The high-frequency properties of the transistor (3) are strongly determined by the size of the conductive mounting surface (2), which through an insulating substrate (1) forms a parasitic capacitance with a conductive ground surface (18), which capacitance is connected to the transistor (3). This parasitic capacitance is very important especially for high-frequency applications. Furthermore, the bonding wires (E, B) for the connection pads of emitter and base are shorter than in the prior art because they need not pass over a relatively large conductive mounting surface (2). Shorter bonding wires provide a lower self-inductance and resistance, which benefits the high-frequency properties and the possibility of supplying more electric power.