A method of forming a microelectronic device comprises forming a sacrificial material over a base structure. Portions of the sacrificial material are replaced with an etch-resistant material. A stack structure is formed over the etch-resistant material and remaining portions of the sacrificial material. The stack structure comprises a vertically alternating sequence of insulative material and additional sacrificial material arranged in tiers, and at least one staircase structure horizontally overlapping the etch-resistant material and having steps comprising horizontal ends of the tiers. Slots are formed to vertically extend through the stack structure and the remaining portions of the sacrificial material. The sacrificial material and the additional sacrificial material are selectively replaced with conductive material after forming the slots to respectively form lateral contact structures and conductive structures. Microelectronic devices, memory devices, and electronic systems are also described.