| 摘要 |
A first aspect of the invention is to realize a power amplifier having high power adding efficiency and high power gain at low cost. For that purpose, in a semiconductor device using an emitter top heterojunction bipolar transistor formed above a semiconductor substrate and having a planar shape in a ring-like shape, a structure is provided in which a base electrode is present only on an inner side of a ring-like emitter-base junction region. In this way, as a result of enabling to reduce base/collector junction capacitance per unit emitter area without using a collector top structure having complicated fabricating steps, a semiconductor device having high power adding efficiency and high-power gain and suitable for a power amplifier can be realized. A second aspect of the application is to provide a power amplifier enabling to reduce temperature dependency of power gain. For that purpose, in a multistage power amplifier including a first amplifier circuit 2 having one or more of bipolar transistors connected in parallel and arranged above a first semiconductor substrate and a second amplifier circuit 3 having one or more of bipolar transistors connected in parallel and arranged above a second semiconductor substrate, the bipolar transistor used in the first amplifier circuit 2 is provided with an emitter shape having a planar shape in a rectangular shape and the bipolar transistor used in the second amplifier circuit 3 is provided with an emitter shape in, for example, a ring-like shape and a base electrode thereof is present only on the inner side of the ring-like emitter.
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