A semiconductor package includes a first package component comprising: a first semiconductor die; a first encapsulant around the first semiconductor die; and a first redistribution structure electrically connected to the semiconductor die. The semiconductor package further includes a second package component bonded to the first package component, wherein the second package component comprises a second semiconductor die; a heat spreader between the first semiconductor die and the second package component; and a second encapsulant between the first package component and the second package component, wherein the second encapsulant has a lower thermal conductivity than the heat spreader.