The process of electromigration in thin Al films was studied directly by transmission electron microscopy during passage of current. Due to electromigration, the Al ions migrate along the test strip from cathode to anode, and the actual opening up of holes near the cathode was observed. The rate of hole formation was used to measure an activation energy. For the test strips, a value of 0.7 eV was obtained. In addition, some physical aspects of hole formation, as well as material buildup in the form of hillocks and single‐crystal Al whiskers, were observed. Some of the whiskers, which were less than 1 &mgr; in diameter, were seen to grow to unusual lengths, occasionally exceeding 50 &mgr;.