ZA3 is a zinc-based alloy with aluminium as its main alloying element. Producing ZA3 product by semisolid metal processing (SSM) can offer significant advantages such as the reduction of macrosegregations, porosity and low forming efforts. The aim of this study was to produce nondendritic semisolid ZA3 alloy through heat treatment. The thermal and microstructure analysis of ZA3 alloy were studied using Differential Scanning Calorimeter (DSC) and Scanning Electron Microscopy (SEM). The solidus and liquidus of the alloy can be determined by DSC analysis. The changes to the microstructures in response to two different isothermal treatments were investigated. They are heating at 100°C for 3-6 h and at 280°C for 0.5-5 h, respectively. Subsequently, all of the treated samples are partially remelt at 383°C for 15 min. The initial as-cast ZA3 alloy consisted of dendritic microstructure typical of a cast ingot. The major effort in the semi-solid technologies is the generation of small and spherical morphologies. The results indicated that when the respective heat-treated ZA3 alloy at 100°C for 4.5 h and 280°C for 3 h was subjected to partial remelting into its semisolid zone, the dendritic arms coalesced and coarsened into fine solid grains of 34±17 μm with corresponds to 0.84 of shape factor and 33±16 μm with the best shape factor of 0.85.