Shape evolution during through-mask electrochemical. micromachining was investigated to study the problem of island formation caused by loss of electrical contact. A mathematical model was developed to predict shape evolution. Laplace’s equation for potential was solved using the boundary element method to determine current distribution at the anode. The current distribution was combined with a moving boundary algorithm to predict the shape of the evolving cavity. The influence of the photoresist artwork dimensions on current distribution at the surface of an evolving feature was investigated. The island formation problem was identified as most Likely to occur with a combination of low aspect ratio and low film thickness ratio. Elimination of the island formation problem is discussed.