Methodist College will play Ballyclare High in the final of the 2012 after beating holders Campbell College 18-8 at Ravenhill on Wednesday.
Rudolph Benade's penalty gave Methody a 3-0 lead at half-time and he was among the try-scorers in the second half as they sealed their semi-final victory.
A try by full-back Jack Owens had Campbell ahead in the second half.
Methody regained the lead when Elliot Mooney got over and they scored further tries through Benade and Chris Gracey.
Ballyclare High beat Wallace High 26-12 in Monday's opening semi-final.
That win, helped by two Andrew Butler tries, earned Ballyclare their first final appearance since 1973.
Butler scored Ballyclare's opening try on 25 minutes before Jonny Holmes added a second try.
Jordan Grattan touched down for Wallace but Butler completed his double to put Ballyclare back in control.
Ballyclare sealed their spot in the 19 March final with a James Beattie try before Grattan went over late on.
Holmes converted three tries to go with his try while he also set up Beattie for Ballyclare's fourth try.