There is provided a water-cooled heat sink including first and second heat transfer channel plates that are stacked and coupled together. The first heat transfer channel plate is provided with a continuous recess that is located in a facing surface thereof that faces the second heat transfer channel plate, corresponds to the coolant channel, and is open at the facing surface, the second heat transfer channel plate is provided with a continuous protrusion, which is fitted into the recess of the first heat transfer channel plate with a gap therebetween, in a facing surface thereof that faces the first heat transfer channel plate, and the first and second heat transfer channel plates are stacked and coupled together to define the coolant channel between the recess and the protrusion.