A microelectronic device includes a substrate having a trench extending therethrough between an active surface thereof and an inactive surface thereof opposite the active surface, a conductive via electrode extending through the substrate between sidewalls of the trench, and an insulating layer extending along the inactive surface of the substrate outside the trench and extending at least partially into the trench. The insulating layer defines a gap region in the trench that separates the substrate and the via electrode. Related devices and methods of fabrication are also discussed.