Abstract: A three-dimensional integrated circuit stack comprises a first integrated circuit structure, a second integrated circuit structure bonding to the first integrated circuit structure, and a redistribution structure. The first integrated circuit structure comprises a first semiconductor device, a first buffer structure, a first interconnect structure, a first conductive via, and a first through via. The first semiconductor device is located between the first buffer structure and the first interconnect structure. The first conductive via is extending through the first buffer structure and in contact with the first semiconductor device. The first through via is extending from the first buffer structure to the first interconnect structure. The redistribution structure is disposed on the first buffer structure, electrically connected to the first semiconductor device through the first conductive via, and electrically connected to the first interconnect structure through the first through via.