Sullivan Upper beat Coleraine Inst 27-14, in a match which saw both sides reduced to 14 men, to reach their first ever Schools' Cup final on Thursday.
Charlie McEwan, Mark Crockford and Josh Davidson scored tries for Sullivan, who were also awarded a penalty try. Mark Adair added seven points with the boot.
Conor Shiels and Mark Gordon touched down for Coleraine, Shiels converting.
Sullivan's Chris Jordan and Jake Scott of Coleraine were sent-off for an off-the-ball incident as tempers flared.
Scrum-Half McEwan put the Holywood side ahead at Queen's after charging down an attempted Coleraine clearance.
Out-half Adair missed the conversion but minutes later made amends by landing a penalty kick.
On the stroke of half-time hooker Crockford touched down after Sullivan's rolling maul put pressure on the Coleraine defence. Adair kicked the conversion to give Sullivan a 15-point advantage at the break.
Minutes into the second half second row Davidson bulldozed his way over the whitewash to score Sullivan's third try of the afternoon.
Inside-centre Shiels touched down and converted his own try to give his side a glimmer of hope but minutes later referee Stuart Gaffikin awarded Sullivan a penalty try converted by Adair.
In the closing stages outside centre Gordon spotted a gap in the Sullivan defence and sprinted towards the touchline to score a consolation try for Coleraine, which was converted by Shiels.
In the closing minutes Jordan and Scott both received red cards for an off-the-ball incident.
Sullivan held on to book their place in the St. Patrick's Day decider against Methodist College at Ravenhill.
Methody beat Wallace High in the first semi-final on Tuesday.