A microelectronic device comprises a first set of tiers, each tier of the first set of tiers comprising alternating levels of a conductive material and an insulative material and having a first tier pitch, a second set of tiers adjacent to the first set of tiers, each tier of the second set of tiers comprising alternating levels of the conductive material and the insulative material and having a second tier pitch less than the first tier pitch, a third set of tiers adjacent to the second set of tiers, each tier of the third set of tiers comprising alternating levels of the conductive material and the insulative material and having a third tier pitch less than the second tier pitch, and a string of memory cells extending through the first set of tiers, the second set of tiers, and the third set of tiers. Related microelectronic devices, electronic systems, and methods are also described.