An embodiment method for forming a semiconductor package includes attaching a first die to a first carrier, depositing a first isolation material around the first die, and after depositing the first isolation material, bonding a second die to the first die. Bonding the second die to the first die includes forming a dielectric-to-dielectric bond. The method further includes removing the first carrier and forming fan-out redistribution layers (RDLs) on an opposing side of the first die as the second die. The fan-out RDLs are electrically connected to the first die and the second die.