The Dunedin school, having one of the greatest seasons in its long history, has beaten Napier Boys' High School 30-16 in Rotorua this afternoon.
Otago Boys' will play Auckland powerhouse St Kentigern in the final next week.
Napier Boys' led 11-0 at halftime but the game changed completely in the second half.
Otago Boys' scored three tries in the space of eight thrilling minutes to take charge of the game.