The use of a special quasirandom structure (SQS) is a rational and efficientway to approximate random alloys. A wide variety of physical properties ofmetallic and semiconductor random alloys have been successfully estimated by a combination of an SQS and density functional theory calculation. Here, we investigate the application of an SQS to the ionic multicomponent systems with configurations of heterovalent ions, including point-charge lattices, MgAl2O4 and ZnSnP2. It is found that the physical properties do not converge with the supercell size of the SQS. This is ascribed to the fact that the correlation functions of long-range clusters larger than the period of the supercell are not optimized in the SQS. However, we demonstrate that the physical properties of the perfectly disordered structure can be estimated by linear extrapolation using the inverse of the supercell size.