A wiring substrate includes a first insulating layer with a first opening, a second insulating layer with a second opening, a high-frequency wiring layer, a first wiring layer, a second wiring layer, and a plurality of conductive pillars. The high-frequency wiring layer including a high-frequency trace is sandwiched between the first insulating layer and the second insulating layer. The first opening and the second opening expose two sides of the high-frequency trace respectively. The high-frequency trace has a smooth surface which is not covered by the first insulating layer and the second insulating layer and has the roughness ranging between 0.1 and 2 μm. The first insulating layer and the second insulating layer are all located between the first wiring layer and the second wiring layer. The conductive pillars are disposed in the second insulating layer and connected to the high-frequency trace.