To model the avalanche breakdown of a voltage regulator diode under reverse bias, a computationally rigorous device physics model using the Monte Carlo method to solve charge carrier Boltzmann transport equations (BTEs) is proposed. The transport of energetic charge carriers is calculated by using the full energy band instead of the non-parabolic band structure. The position-dependent doping profile found in real diodes is modeled accurately and time-efficiently. A two-step method is introduced to accelerate the simulation of avalanche breakdown. With the proposed model, the expected IV characteristics of a voltage regulator diode under reverse bias are simulated. The transport of charge carriers and avalanche breakdown are modeled at the microscopic level, and the simulation results are verified through comparison with the IV characteristics from the datasheet. This model can be used to analyze device susceptibility to electrical stress, providing a graphical visualization for failure mechanisms.