We report our simulation results for the dynamic characteristics of single-transit SiC SiC impact-ionization avalanche transit-time (IMPATT) diodes. An iterative Monte Carlo-Crank-Nicholson technique has been used to solve the coupled electron transport-heat conduction problem. This procedure allows for accurate computation of both the device current as a function of temperature, time, and position, and the internal heat generation. The technique is quite general, has not been used before, and can be applied for the analysis of any power device. Our results show that the internal power generation profile within the SiC IMPATT device can have a very nonuniform axial distribution. The internal heating is seen to significantly degrade the device efficiency and optimum operating frequency. With thermal effects the output current values are lower and the transit time is increased.