A microelectronic device comprises a stack structure comprising a stack structure comprising a vertically alternating sequence of conductive structures and insulative structures arranged in tiers, the stack structure divided into block structures separated from one another by slot structures, strings of memory cells vertically extending through the block structures of the stack structure, the strings of memory cells individually comprising a channel material vertically extending through the stack structure, an additional stack structure vertically overlying the stack structure and comprising a vertical sequence of additional conductive structures and additional insulative structures arranged in additional tiers, first pillars extending through the additional stack structure and vertically overlying the strings of memory cells, each of the first pillars horizontally offset from a center of a corresponding string of memory cells, second pillars extending through the additional stack structure and vertically overlying the strings of memory cells, and additional slot structures comprising a dielectric material extending through at least a portion of the additional stack structure and sub-dividing each of the block structures into sub-block structures, the additional slot structures horizontally neighboring the first pillars. Related microelectronic devices, electronic systems, and methods are also described.