A power amplifier, for example a class-E switching power amplifier, and corresponding method, comprising: a plurality of power transistors (16), for example twelve power transistors, providing a partitioned power transistor; and a voltage sensing module (22), comprising for example voltage dividers and inverters, digitally sensing the drain voltage (2) of the partitioned power transistor to control the number of power transistors of the plurality of power transistors (16) that are switched on or off thereby controlling the drain voltage (2) which is varying for example due to antenna mismatch. The power amplifier may further comprise a memory (24) coupled to the voltage sensing module (22) for storing a history of the drain voltage (2), e.g. a history of antenna mismatch.