A facile fabrication of a hetero-sized nanocluster array has been demonstrated by using inert-gas condensation at room temperature. The array consisted of 1.5 and 3.2 nm sized gold clusters. The nonvolatile memory characteristics of a memory cell that had a hetero-sized nanocluster array to be used as a charge-trapping layer were compared to those of two cells that had 1.5 and 3.2 nm sized cluster arrays, respectively. While the average cluster size or the average number of electrons trapped in a cluster was reflected in the programming/erasing characteristics, the nanostructure effect was revealed in the retention characteristics, i.e. the proposed cell was found to have the gentlest degradation of the memory window. This can be explained by a preferential pathway for charge-carrier redistribution, caused by the ionization potential difference between the two nanoclusters of different sizes.