Bonding and isolation techniques for stacked device structures are disclosed herein. An exemplary method includes forming a first insulation layer on a first device component, forming a second insulation layer on a second device component, and bonding the first insulation layer and the second insulation layer. The bonding provides a stacked structure that includes the first device component over the second device component, and an isolation structure (formed by the first insulation layer bonded to the second insulation layer) therebetween. The isolation structure includes a first portion having a first composition and a second portion having a second composition different than the first composition. The method further includes processing the stacked structure to form a first device disposed over a second device, where the isolation structure separates the first device and the second device. The first insulation layer and the second insulation layer may include the same or different materials.