A circuit board includes a first external circuit layer, a first substrate, a second substrate, a third substrate, and a conductive through hole structure. The first substrate includes conductive pillars electrically connecting the first external circuit layer and the second substrate. The second substrate has an opening and includes a first dielectric layer. The opening penetrates the second substrate, and the first dielectric layer fills the opening. The third substrate includes an insulating layer, a second external circuit layer, and conductive holes. A conductive material layer of the conductive through hole structure covers an inner wall of a through hole and electrically connects the first and the second external circuit layers to define a signal path. The first external circuit layer, the conductive pillars, the second substrate, the conductive holes and the second external circuit layer are electrically connected to define a ground path surrounding the signal path.