The electromigration accelerating factors are critically dependent on the absolute temperature of the conductor. This temperature is governed by the ambient background temperature and the temperature rise due to the elevated current. A first-order model of steady state Joule heating within small-geometry VLSI metallizations has been developed. By careful consideration of t h e first-order relationships between conductor resistance, current and temperature it Is possible to extract parameters in order to characterize the metal conductors. A first-order model has been tested against predictions from planar aluminium, 1% silicon (Aljl% Si) structures with a confidence limit of 99%.