A circuit structure includes an inner circuit layer, a first and a second dielectric layers, a first and a second conductive material layers, and a second and a third conductive layers. The first dielectric layer covers a first conductive layer of the inner circuit layer and has a first surface and first circuit grooves. The first conductive material layer is disposed inside the first circuit grooves. The second conductive layer is disposed on the first surface and includes a signal trace and at least two reference traces. The second dielectric layer covers the first surface and the second conductive layer and has a second surface and second circuit grooves. Widths of the first and the second circuit grooves are smaller than that of the reference traces. The second conductive material layer is disposed inside the second circuit grooves. The third conductive layer is disposed on the second surface.