Provided is an electromagnetic bandgap (EBG) structure, and particularly, an overlay EBG structure in which a plurality of vias and a plurality of plates are formed at intervals on a central signal line in such a manner that the vias and plates extend vertically from a substrate in order to reduce leakage loss of an electromagnetic wave through the substrate. Therefore, it is possible to prevent an electromagnetic wave passing through a transmission line from being lost through the substrate, to obtain desired frequency characteristics by adjusting the dimensions of the vias and plates, and to manufacture the overlay EBG structure using an existing CMOS process without having to perform any additional process.