Electromigration failure at contacts and vias is the potential limitation of interconnect reliability in multilevel structures. In two-level structures, it has been found that the upper and lower metal levels exhibit different electromigration failure characteristics; the latter fails predominantly. In this work, we have systematically studied the critical current densities: of the lower and upper level conductors terminated at W-plug vias. We found that the critical current density for the upper level is significantly higher. The effect of passivation layer on the critical current density is discussed.