The semifinal concept, similar to the one used in Eurovision Song Contest, was introduced in NSC 6. Up to and including NSC 17, the semifinal was a single event in which the top scoring nations qualified to make up one half of the final, the other half consisting of nations prequalified based on their result in the previous edition. Starting with NSC 18, the semifinal was changed to the current dual semifinal system, also in tandem with the Eurovision Song Contest. Apart from the top 6 of the previous edition, who are prequalified for the final, the two semifinals contain all the participating nations randomly divided. The top ten entries qualify from each semifinal, plus one extra wild-card per semi, decided by the Rest Jury consisting mainly of optional votes from the participants of the other semifinal.
Voting is done in the exact same way as the final, but the full results are kept secret until the whole contest is finished. The qualifiers are announced in random order, after which the place and total score of all eliminated nations (as well as the total score of the lowest qualified country) is revealed.
- Salona was the only nation to never participate in a semifinal, as they withdrew from the contest prior to their introduction.