We present PMC-3D, a parallel three-dimensional (3-D) Monte Carlo device simulator for multiprocessors. The parallel algorithm is an extension of the standard Monte Carlo device simulation model in 3-D, in which the particle dynamics generated from the stochastic Monte Carlo method are solved simultaneously with Poisson's equation on a 3-D mesh using finite differences. Due to the large computational requirements of 3-D device simulation, it is necessary to parallelize both the Poisson solver and the Monte Carlo simulation phase of the device simulator. The parallel algorithms were implemented on a 1024-node distributed memory nCUBE multicomputer and a 4-mode shared memory Ardent multiprocessor. We validate the accuracy of our implementations by generating the static characteristics of a MESFET and present test results on the fixed and scaled speedups obtained on the two types of parallel computers. Improvements in performance are observed utilizing dynamic load balancing for the distributed memory case.>