A package structure includes a first dielectric layer, a first semiconductor device over the first dielectric layer, a first redistribution line in the first dielectric layer, a second dielectric layer over the first semiconductor device, a second semiconductor device over the second dielectric layer, a second redistribution line in the second dielectric layer, a conductive through-via over the first dielectric layer and electrically connected to the first redistribution line, a conductive ball over the conductive through-via and electrically connected to the second redistribution line, and a molding material. The molding material surrounds the first semiconductor device, the conductive through-via, and the conductive ball, wherein a top of the conductive ball is higher than a top of the molding material.