Electron cyclotron resonance (ECR) reactors are now being investigated for use in the plasma processing of semiconductors. The attractive feature of ECR excitation is that high plasma densities (1010–1012cm−3) can be obtained at low pressures (0.1–a few mTorr). In this paper, we present results from a computer simulation of the electron kinetics in ECR reactors. The model is a multidimensional Monte Carlo simulation coupled with a fluid simulation with which the electron energy distribution (EED) may be calculated. We find that the electron temperature (Te=2/3⟨&egr;⟩) in Ar plasmas (0.1–10 mTorr, 100s W) is 10–20 eV in the ECR zone, falling to a few to 5 eV downstream of the ECR zone, in general agreement with experiments. The EED can be described as being multitemperature with a low energy component (5–10 eV) and a high energy tail extending to many 10sto 100s eV. Predicted ambipolar potentials are 10–30 V, increasing with decreasing pressure and increasing power deposition.