A large defect ([inverted lazy s]600 &mgr; in diameter) was observed to move below the surface in aluminum thin film at a velocity in excess of 40 &mgr;/h (1.11×10−8m/sec). X‐ray stress topography was used to trace the migration, which was in the direction of electron flow, with dislocations in the silicon (under the aluminum) serving as location references for measuring the velocity. The migration direction and velocity of the subsurface defect were reproduced by forming an Al&sngbnd;Sn eutectic zone in the central part of an aluminum stripe. The movement of a liquid alloy inclusion in solid aluminum film under an electromigration driving force was proposed to explain the experimental observations.