A bonded assembly includes a first semiconductor die containing a first substrate, first semiconductor devices, and first bonding pads laterally surrounded by a first pad-level dielectric layer. The first pad-level dielectric layer includes at least one first encapsulated airgap located between neighboring pairs of first bonding pads and encapsulated by a first dielectric fill material of the first pad-level dielectric layer. The bonded assembly includes a second semiconductor die containing a second substrate, second semiconductor devices, and second bonding pads laterally surrounded by a second pad-level dielectric layer. Each of the second bonding pads is bonded to a respective one of the first bonding pads.