The passage of an electric current in a material can cause a biased mass transport at its surface. This migration phenomenon is intimately related to the microscopic details of atomic processes of diffusion and attachment/detachment at step edges. Using low-energy electron microscopy, we have examined in operando under an electric current the migration of Si(111)-1 × 1 advacancy islands confined on Si(111)-7 × 7 terraces. The islands move opposite to the current direction, with velocity increasing with the radius. The effective valence of Si adatoms is 2.8 ± 0.5 and the kinetic length of attachment-detachment is about 500 nm. The analysis of the island’s shape reveals that the electric current significantly biases the kinetic rate of mass transfers at step edges modifying the overall island’s shape.