A heatsink with an internal cavity for liquid cooling includes: a first part having a first group of fins extending into the internal cavity; a second part attached to the first part so that the internal cavity is formed, the second part having a second group of fins that extend into the internal cavity and that are configured to fit among the first group of fins; an inlet into the internal cavity on at least one of the first and second parts; and an outlet from the internal cavity on at least one of the first and second parts.