Recently, it was found that electromigration‐induced failure of metallic interconnects in integrated circuits occurs when rounded voids deform into narrow slitlike voids, which are often transgranular. The mechanism of this shape change is now examined by numerical simulation on the basis of electromigration‐driven surface diffusion. As a result, it is found that shape change and motion of voids are competing processes. Large voids with respect to the linewidth are deformed by the electron wind whereas small voids move without any shape changes. Combining diffusional anisotropy with electron wind dynamics allows the experimentally observed faceting of even small voids to be reproduced in the simulation. ©1995 American Institute of Physics.