A wiring structure includes an upper conductive structure, a lower conductive structure, an adhesion layer and at least one outer via. The upper conductive structure includes at least one dielectric layer and at least one circuit layer in contact with the dielectric layer. The lower conductive structure includes at least one dielectric layer and at least one circuit layer in contact with the dielectric layer. The adhesion layer is interposed between the upper conductive structure and the lower conductive structure to bond the upper conductive structure and the lower conductive structure together. The outer via extends through at least a portion of the upper conductive structure and the adhesion layer, and electrically connected to the circuit layer of the lower conductive structure.