Power amplifier and compound semiconductor device

A power amplifier comprising:

• an initial-stage amplifier circuit comprising:
• a first high electron mobility transistor having a source electrically connected to a reference potential, and a gate to which a radio-frequency input signal is input, and
• a first heterojunction bipolar transistor having an emitter electrically connected to a drain of the first high electron mobility transistor, a base electrically connected to the reference potential in an alternate-current fashion, and a collector to which direct-current power is supplied and from which a radio-frequency signal is output;
• an output-stage amplifier circuit comprising:
• a second heterojunction bipolar transistor having an emitter electrically connected to the reference potential, a base to which the radio-frequency signal output from the first heterojunction bipolar transistor is input, and a collector to which direct-current power is supplied and from which a radio-frequency output signal is output;
• an initial-stage bias circuit configured to output a first bias voltage to the gate of the first high electron mobility transistor and a second bias voltage to the base of the first heterojunction bipolar transistor;
• and
• an output-stage bias circuit configured to output a third bias voltage to the base of the second heterojunction bipolar transistor.