In this study, electromigration (EM) characteristics of Cu line and nickel (Ni)-silicide on Cu-line/W-via/Ni-silicide structure were compared. The experimental results revealed that EM competition of Cu line depletion and Ni-silicide migration depends on the length of Cu line and the stress current density. For a longer Cu line or stress at a higher current density, the failure time of Cu-line depletion is lower than that of Ni-silicide migration because the failure mode is Cu-line depletion. On the other hand, as the length of Cu line is decreased and stressed at a lower current density, the failure mode is transferred to Ni-silicide migration due to a stronger back-stress effect in a shorter Cu line. The critical current densities , activation energy , and current density exponent values for Cu-line depletion mode and Ni-silicide migration modes were characterized, which are used to predict the EM lifetime at normal operation conditions. The results indicated that although the failure time of Ni-silicide migration mode is lower than that of Cu-line depletion mode for a shorter Cu line at a higher stress temperature, Ni-silicide migration with a higher activation energy results in a longer EM lifetime at a lower operation temperature.