There is provided a wiring substrate. The wiring substrate includes: a first wiring layer; a first insulating layer on the first wiring layer; a first coupling agent layer on the first insulating layer; a first copper/tin alloy layer on the first coupling agent layer; a first via hole formed through the first copper/tin alloy layer, the first coupling agent layer, and the first insulating layer to reach the first wiring layer; a metal catalyst provided on only a sidewall of the first via hole; a seed layer provided on the metal catalyst and formed only on the sidewall of the first via hole; and a metal plating layer formed on the first copper/tin alloy layer and the seed layer and filled in the first via hole to contact the first wiring layer.