Abstract: Power amplifiers with supply capacitor switching are provided herein. In certain configurations, a power amplifier system includes a power amplifier that provides amplification to a radio frequency (RF) signal, a power management circuit that controls a voltage level of a supply voltage of the power amplifier, a supply capacitor, and a silicon-on-insulator (SOI) switch in series with the supply capacitor between the supply voltage and the a reference voltage, such as ground. The power management circuit is operable in multiple supply control modes including, for example, an average power tracking (APT) mode and an envelope tracking (ET) mode. Additionally, the SOI switch is controlled based on the supply control mode of the power management circuit.