The solid-state reactions of electroplated gallium thin films with copper, gold and molybdenum were investigated using XRD, SIMS, TEMEDS and linear strip voltammetry. Due to the low melting temperature of gallium metal, the activation energy for gallium diffusion is lower than the other metals used. Hence Ga diffuses faster and reacts to form alloy phases with the other metals investigated. In a thin film stack of Ga with another metals (Me), (Me = Cu, Au and Mo), equilibrium compounds are formed, which compounds form depends on the relative composition and diffusion time. If there is excess Ga, or excess Me, it can further react with the metastable compounds to form an equilibrium compound. In addition, TaN was found to act as an effective barrier layer to gallium diffusion. © 2011 The Electrochemical Society.