Peak detecting cascode for breakdown protection. In some embodiments, a power amplifier can include an amplifying transistor configured to amplify a radio-frequency (RF) signal, and a bias circuit coupled to a bias node of the amplifying transistor and configured to yield a bias voltage at the bias node. The power amplifier can further include a bias adjustment circuit that couples an output node of the amplifying transistor and the bias circuit. The bias adjustment circuit can be configured to adjust the bias voltage in response to a potential difference between the output node and the bias node exceeding a threshold value.