It is demonstrated that with proper analysis of the diffusion profiles, the effective charge and diffusivity for grain‐boundary electromigration can be separately measured. Electromigration profiles are analyzed based on Fisher‐type approximations for an equiaxial and perfectly textured grain structure. Electromigration profiles were obtained for Cu in Al at 255°C by measuring the spreading of a Cu cross‐stripe subject to a direct current; the results were checked by annealing experiments performed under similar conditions. Cu was observed to migrate in the direction of electron flow. Results obtained from analysis of the anode and annealing profiles are −16.8±1.2 for the effective charge and (1.75±0.12) × 10−14cm3/sec for the diffusivity parameter &agr;Db&dgr;. The over‐all consistency of the results is better than 5%. Whipple analysis gives a more exact value of (2.74±0.16) × 10−14cm3/sec for &agr;Db&dgr;.