A semiconductor package includes a substrate, a composite seed-barrier layer, a routing via, and a semiconductor die. The substrate has a through hole formed therethrough. The composite seed-barrier layer extends on sidewalls of the through hole and includes a first barrier layer, a seed layer, and a second barrier layer sequentially stacked on the sidewalls of the through hole. The routing via fills the through hole and is separated from the substrate by the composite seed-barrier layer. The semiconductor die is electrically connected to the routing via. Along the sidewalls of the through holes, at a level height corresponding to half of a total thickness of the substrate, the seed layer is present as inclusions of seed material surrounded by barrier material of the first barrier layer and the second barrier layer.