Friday's convincing win over the Finns was the Russians' revenge for the 7-4 defeat to their Nordic neighbors on the opening day of the tournament.
The U.S. team beat defending champions Canada 2-1 in the other semifinal. The final and the bronze-medal playoff will take place Sunday in Fargo, North Dakota.
Russia was inspired to victory by Yevgeny Kuznetsov's goal and three assists, as well as an outstanding performance by goalkeeper Igor Bobkov, who recorded a shutout despite the Finns out-shooting their opponents 51-45.
Russia is the most successful side in the history of the International Ice Hockey Federation's Under-18 championships and now will add another medal to its three golds and three silvers and one bronze.