Illustrative embodiments of power amplifiers are disclosed. In one embodiment, a power amplifier includes a plurality of transistors formed on a silicon-on-insulator (SOI) substrate such that the plurality of transistors are each electrically isolated from one another within the SOI substrate. The power amplifier also includes a plurality of biasing networks, each biasing network being configured to dynamically bias at least one of the plurality of transistors. The plurality of transistors are electrically coupled in a series stack, with an output of the power amplifier being provided across the series stack.