A variable-bias power amplifier is provided, comprising: a first variable voltage source generating first bias voltages based on bias control signals; a first amplifier circuit amplifying an output RF signal to generate a first amplified signal based on the first bias voltages; a second variable voltage source generating second bias voltages based on the bias control signals; a second amplifier circuit amplifying the output RF signal to generate a second amplified signal based on the second bias voltages; and a DC isolation circuit between the first amplifier circuit and the second amplifier circuit, electrically isolating DC currents at the first amplifier from DC currents at the second amplifier, wherein the first variable voltage source can be controlled independently from the second variable voltage source, and the first amplifier circuit, the second amplifier circuit, and the DC isolation circuit are all formed on a single die.