A nonlinear least-squares fitting procedure for array model parameter extraction using field emission (FE) data has been developed and extensively applied for Si and Si/HfC-coated arrays with 1024, 4000, and 16 000 tips measured in ultrahigh vacuum conditions. The array FE model is built up using equations that describe the electron emission current from individual emitters of given radius R and work function phi together with nonuniform distribution functions giving the dispersion of these parameters within the array. A combined numerical/analytical approach is used to accurately express the electric field for the actual gated emitter configuration. The FE cur-rent is computed through integration of the current density over the emitter tip surface and as a sum of all tip currents in the array. The program, developed as a MATHCAD application using the intrinsic "minerr" routine, extracts array parameters of physical interest and does not make use of "area" and "field enhancement" factors. HfC-coated FE arrays perform better than (noncoated) Si arrays when comparing the total emission current, the spatial uniformity and number of active tips, and the stability in long-term operation. (C) 2004 American Vacuum Society.