A power amplifier circuit includes a first transistor, a capacitor, and a second transistor. The first transistor has an emitter electrically connected to a reference potential, a base, and a collector electrically connected to a first power supply potential. A first end of the capacitor is electrically connected to the collector of the first transistor. The second transistor has an emitter electrically connected to a second end of the capacitor and electrically connected to the reference potential, a base, and a collector electrically connected to the first power supply potential. An RF output signal obtained by amplifying the RF input signal is output from the collector of the second transistor. A second bias circuit includes a third transistor having a collector electrically connected to a second power supply potential, a base, and an emitter from which the second bias current or voltage is output.

A power amplifier circuit includes a first transistor that amplifies an RF signal; a bias current source that supplies a bias current to a second terminal of the first transistor through a first current path; and an adjustment circuit that adjusts the bias current in accordance with a variable power-supply voltage supplied from a power-supply terminal. The adjustment circuit includes first to third resistors, and an adjustment transistor including a first terminal connected to the power-supply terminal through the first resistor, a second terminal connected to the bias current source through the second resistor, and a third terminal connected to the first current path through the third resistor. When the variable power-supply voltage is not less than a first voltage and not greater than a third voltage, the adjustment circuit increases a current that flows to the power-supply terminal through a second current path as the variable power-supply voltage decreases.

A power amplifier circuit includes a first transistor having a base or gate connected to a signal path, an emitter or source grounded via a first conductor, and a collector or drain, the first transistor amplifying an input signal supplied to the base or gate thereof along the signal path and outputting the amplified signal from the collector or drain thereof; a first element in a preceding stage of the first transistor, the first element having a first end connected to the signal path such that the first element is connected along a path branched from the signal path, and a second end grounded via a second conductor; and a first capacitor having a first end connected to a node between the emitter or source of the first transistor and the first conductor, and a second end connected to a node between the first element and the second conductor.