A microelectronic device comprises a stack structure, first dielectric-filled trenches extending vertically through the stack structure, and at least one second dielectric-filled trench intersecting the first dielectric-filled trenches. The stack structure comprises a vertically alternating sequence of conductive material and insulative material arranged in tiers. The first dielectric-filled trenches divide the stack structure into blocks and extend horizontally in a first direction. At least one second dielectric-filled trench extends horizontally in a second direction orthogonal to the first direction. At least one second dielectric-filled trench has boundaries defined by at least one staircase structure having steps defined by horizontal ends of the tiers in the first direction. Memory devices and electronic systems are also described.