A microelectronic device includes a stack structure, a staircase structure, composite pad structures, and conductive contact structures. The stack structure includes vertically alternating conductive structures and insulative structures arranged in tiers. Each of the tiers individually includes one of the conductive structures and one of the insulative structures. The staircase structure has steps including edges of at least some of the tiers of the stack structure. The composite pad structures are on the steps of the staircase structure. Each of the composite pad structures includes a lower pad structure, and an upper pad structure overlying the lower pad structure and having a different material composition than the lower pad structure. The conductive contact structures extend through the composite pad structures and to the conductive structures of the stack structure. Memory devices, electronic systems, and methods of forming microelectronic devices are also described.