A microelectronic device comprises a stack structure comprising a vertically alternating sequence of conductive structures and insulative structures arranged in tiers, a staircase structure comprising steps comprising horizontal edges of the tiers, each of the steps comprising multiple tiers, and conductive contact structures vertically extending from a vertically upper surface of the stack structure to the conductive structures of the steps, the conductive structures defining each of the steps individually in contact with a conductive contact structure. Related memory devices and electronic systems are also described.