This paper describes the heat treatment effect on the eutectic silicon evolution in the A357 alloy, obtained by semisolid forming process (SSM). The coarsening rate of the silicon was determined by Image Analysis Technique in specimens from rheocasting ingots and thixocasting components. The study was realized in the temperature range from 450 to 550°C by applying heating times between 1 and 24 hours. The results show that during the heat treatment the coarsening and sphereodization of the silicon particles is produced and the fragmentation stages, which are observed in conventional alloys, do not appear. Kinetic silicon growth has been adjusted to the Oswald’s ripening equation.