A method of forming a microelectronic device includes forming a microelectronic device structure. The microelectronic device structure includes a stack structure having an alternating sequence of conductive structures and insulative structures, an upper stadium structure, a lower stadium structure, and a crest region defined between a first stair step structure of the upper stadium structure and a second stair step structure of the lower stadium structure. The stack structure further includes pillar structures extending through the stack structure and dielectric structures interposed between neighboring pillar structures within the upper stadium structure. The method further includes forming a trench in the crest region of the stack structure between two dielectric structures of the dielectric structures on opposing sides of another dielectric structure and filling the trench with a dielectric material. The trench partially overlaps with the dielectric structures.