A contact pad structure includes alternately stacked N insulating layers (N‰¥6) and N conductive layers, and has N regions arranged in a 2D array exposing the respective conductive layers. When the conductive layers are numbered as first to N-th from bottom to top, the number (Ln) of exposed conductive layer decreases in a column direction in the regions of any row, the difference in Ln is fixed between two neighboring rows of regions, Ln decreases from the two ends toward the center in the regions of any column, and the difference in Ln is fixed between two neighboring columns of regions.