We report the simulation of the large-signal performance of mm-wave FET power amplifiers obtained for the first time through Full Band Monte Carlo particle-based device simulation self-consistently coupled with a Harmonic Balance (HB) frequency domain circuit solver. Due to the iterative nature of the HB algorithm, this FET simulation approach is possible only due to the computational efficiency of our Cellular Monte Carlo (CMC), which uses pre-computed scattering tables. On the other hand, a frequency domain circuit solver such as HB allows the simulation of the steady-state behavior of an external passive reactive network without the need for simulating long transient time (i.e. RC, L/C time constants) typical of time domain solutions. By exploiting this newly developed self-consistent CMC/HB code, we were able to time-efficiently characterize the mm-wave power performance of a state-of-the-art 30-nm gate-length InAlN/GaN HEMT.