The field electron energy distributions were investigated for field emission from semiconductors as well as metals. The average energy and the standard deviation As of the distributions were obtained analytically using the WKB transmission coefficient. The obtained analytic forms of and Delta epsilon are found to be useful to characterize field emission. In particular, 2 Delta epsilon represents the width of field electron energy distribution. As the field increases, it increases for metals and n-type semiconductors while it decreases for n-type semiconductors. (c) 2006 American Vacuum Society.