In a semiconductor device using an emitter top heterojunction bipolar transistor
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. This allows reduction of base/collector junction capacitance per unit emitter
area, whereby a semiconductor device having high power adding efficiency and high
power gain suitable for a power amplifier can be realized. Further, in a multistage
power amplifier including first and second amplifier circuits each having one or
more of bipolar transistors, a bipolar transistor in the first amplifier circuit
uses an emitter having a planar shape in a rectangular shape, and a bipolar transistor
in the second amplifier circuit uses an emitter having a ring-like shape and a
base electrode only on the inner side of the emitter.