A microelectronic device comprises a stack structure comprising blocks separated from one another by dielectric slot structures. At least one of the blocks comprises two crest regions, a stadium structure interposed between the two crest regions in a first horizontal direction, and two bridge regions neighboring opposing sides of the stadium structure in a second horizontal direction. A filled trench vertically overlies and is within horizontal boundaries of the stadium structure of the at least one of the blocks. The filled trench comprises a dielectric liner material on the opposing staircase structures of the stadium structure and on inner sidewalls of the two bridge regions, and dielectric structures on and having a different material composition than the dielectric liner material. The dielectric structures are substantially confined within horizontal areas of the steps of the stadium structure. Memory devices, electronic systems, and methods of forming microelectronic devices are also described.