The formation and growth of holes and hillocks at grain boundary triple junctions in thin‐film conductors of gold on gallium arsenide and thin‐film conductors of aluminum‐1 wt. % silicon on (oxidized) silicon during the early stages of electromigration have been investigated through measurement of fractional change of electrical resistance &Dgr;R/Rand microstructural characterization by scanning and transmission electron microscopy. Each grain boundary triple junction is characterized by a unique structure factor &Dgr;Y, which defines the degree of cumulative flux divergence and, consequently, the degree of susceptibility to formation and growth of holes or hillocks. Resultant holes are characterized by a shape factor  f, which defines the degree of noncircularity and, consequently, relates fractional change of hole area to &Dgr;R/R. Estimates of the upper limit for &Dgr;Yand the average value of  f  are in good agreement with measured values of &Dgr;R/Rand consistent with observed microstructure.