A die stack structure including a first semiconductor die, a second semiconductor die, an insulating encapsulation and a redistribution circuit structure is provided. The first semiconductor die includes a first semiconductor substrate including a first portion and a second portion, a first interconnect structure and a first bonding structure. The first interconnect structure is disposed on a top surface of the second portion, a lateral dimension of the first portion is greater than a lateral dimension of the top surface of the second portion. The second semiconductor die is disposed on the first semiconductor die and includes a second bonding structure, the second semiconductor die is electrically connected with the first semiconductor die through the first and second bonding structures. The insulating encapsulation is disposed on the first portion and laterally encapsulating the second portion and the second semiconductor die. The redistribution circuit structure is electrically connected with the first and second semiconductor dies, and the lateral dimension of the first portion is greater than a lateral dimension of the redistribution circuit structure.