One of the major issues in fabricating Al alloy composites reinforced with SiC particulates is to avoid interfacial reaction products, i.e., Al4C3 and Si. The formation of such interfacial reaction products can be suppressed by the presence of an adequate amount of Si within the matrix of the composites. The equilibrium Si contents required to prevent the interfacial reaction in various SiCp/wrought Al composites were predicted both using theoretical calculations and experiments. Application of these results for designing the matrix alloy and selecting process parameters for the semi-solid forming was demonstrated.