Field emission arrays (FEAs) are good candidates for the use as field emitters. The field emission due to quantum mechanical tunneling is described by the well-known Fowler-Nordheim (FN) equation. The FN plots are widely employed to fit the experimental data. In recent experiments of field emission arrays, the results show that the FN plots become nonlinear and are apart from the prediction of the conventional FN theory. In this work, space charge effects on the I-V characteristics of the FEAs that may be operated at high current density are investigated. Within the framework of the effective work function approximation, a good fit to the I-V characteristics of FEAs can be generated by solving the FN equation and Poisson's equation for planar space-charge-limited field emission self-consistently. This solution has been verified by the finite-difference time-domain particle-in-cell simulation. The theoretical results also show good agreement in comparison with some experimental results. This indicates that the space charge effects play an important role in the saturation behavior of field emission arrays. (c) 2007 American Vacuum Society.