An apparatus, comprising an input transformer; a first differential transistor pair configured to receive a first back gate bias voltage; a second differential transistor pair configured to receive a second back gate bias voltage; a cross-coupled neutralization cap comprising PMOS or NMOS transistors and configured to receive a third back gate bias voltage; and an output transformer. A method of fixing at least one back gate bias voltage to impart a desired capacitance to the transistors of at least one of the first differential transistor pair, the second differential transistor pair, or the neutralization cap. The apparatus and method may provide a power amplifier having improved linearity and efficiency.