An energy approach is proposed to describe electromigration induced void nucleation based on phase transformation theory.The chemical potential for an individual migrated atom is predicted by diffusion induced back stress equivalent principle.After determining the chemical potential for the diffusing atoms,the Gibbs free energy controlling the void nucleation can be determined and the mass diffusion process is considered.The critical void radius and nucleation time are determined analytically when the Gibbs free energy approaches the extreme value.The theoretical predictions are compared with the experimental results from literatures and show good accuracy.The proposed model can also be applied to other diffusion induced damage processes such as thermomigration and stress migration.