They have opened up the possibility of the most remarkable final in the history of the tournament.
The Belfast school's second eleven are already in the last four - and both sides have been drawn apart.
The first eleven will travel to Foyle and LondonderryCollegeand the Seconds will be at home to Belfast High School.
The games will be played by Wednesday, June 6, and the final is scheduled for June 20. It's the first time two teams from the same school have reached the semi finals and should they make it to the final it would be a record that can't be beaten.
The "Inst" first eleven made light work of Royal School Armagh in the last of the quarter finals, winning by nine wickets, and the game against Foyle promises to be one of the best of the tournament.
The second eleven will have a particularly tough task ahead against aBelfastHigh Schoolside that includes Irish Under 19 international Paul Stirling. He scored a century against Strabane Grammar Schoolin the quarter finals.
Quarter finals details:
Foyle & Londonderry College beat Bangor GS by by 60 runs. Foyle 190 for 8 (S Clarke 101, D McCarter 46, A Nixon3/43, R Law 2/37). Bangor GS 130 (M Nixon 61, G McCarter 5/23, S Clarke 2/26).
RBAI II beat Ballyclare HS by 47 runs. RBAI II 150 for 9 (R Sheard 21, R Smith 5/23). Ballyclare HS 103 (J Jackson 22, D McCandless 3/15). RBAI II won by 47 runs.
Belfast HS beat Strabane GS by 6 wkts. Strabane GS 158 for 7 (D Curry 42, I Buchannan 27, R Spence 3/26, P Stirling2/34). BelfastHS 159 for 4 (P Stirling107*, A Lynch 2/24).
RBAI beat RS Armagh by 9 wkts. RS Armagh 78 (H Doyle 16, M Wright 14, R McCurry 3/15) RBAI 79 for 1 (R McCarthy 43no, H Doyle 1/39).
Semi final draw:
- Foyle and LondonderryCollegev RBAI
- RBAI II v Belfast HS
