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 ΔR/R and microstructural characterization by scanning and transmission electron microscopy. Each grain boundary triple junction is characterized by a unique structure factor ΔY, 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 ΔR/R. Estimates of the upper limit for ΔY and the average value of f are in good agreement with measured values of ΔR/R and consistent with observed microstructure.