Hischier's international tournament was the 2015 IIHF World U18 Championships, hosted in his native Switzerland. Hischier scored one goal as the Swiss team finished fourth overall. He next played in the 2015 Ivan Hlinka Memorial Tournament, a tournament not regulated by the International Ice Hockey Federation but still considered a major event for under-18 players; Hischier recorded six points over four games. At the 2016 IIHF World U18 Championships he had four points as Switzerland placed eighth.