Pd nanocrystals (NCs) on asymmetric tunnel barrier (ATB) composed of stacked SiO2 and HfO2 layers have been employed for nonvolatile memory devices. The Pd-NC layers are formed by electrostatic self-assembly of negatively charged colloidal Pd NCs. The presence of isolated Pd NCs of ∼5 nm embedded in HfO2 is confirmed by scanning and transmission electron microscopy images. Outstanding program/erase (P/E) properties from C-V curves are observed with a memory window of 6 V under ±17 V. Extrapolation of the data up to ten years shows that the flatband voltage drops at the P/E levels are maintained within only 1.0/0.5 V, respectively, resulting from the efficient data retention based on the ATB. These results are promising enough for the memory structure to be utilized for the multilevel charge storage.