Time characteristics have been simulated numerically both for n- and p-channel memory based on Ge/Si hetero-nanocrystals. Owing to the advantages of the staircase potential barrier and the higher band offset on valence band, the retention time of the memory could achieve the increase of several orders while the programming time still hold the same order approximately, compared with the memory based on Si nanocrystals. Therefore, the present memory device would be expected to solve the contradiction between high-speed programming and long retention time. If so, this type of device would be a promising nonvolatile memory for future VLSI. (C) 2003 Elsevier B.V. All rights reserved.