An empirical large-signal model for high-power microwave silicon-carbide MESFETs capable of predicting self-heating thermal behavior is presented. A generalized drain-current equation based on pulsed-gate IV characteristics measuring up to 2 A and 58 V is presented along with its dependence on temperature. A thermal subcircuit with a nonlinear thermal resistance characterized by a dc method is used to model the temperature behavior of the device. The effect of substrate trapping is modeled as a gate–source voltage correction. The complete drain-current model accurately predicts pulsed-gate and pulsed-gate-and-drain IV characteristics for various quiescent biases, as well as static IV characteristics. The complete large-signal model is shown to accurately predict -parameters, large-signal output, and input reflected power across biases and frequencies, and third-order intermodulation products.