The parish side moved into the last four of the competition after a five-wicket victory achieved with an over to spare.
St John will now play Division I Beeches next Monday with the other semi being Division II St Helier RFC against Division I leaders Abacus.
Last night Beeches defeated JUBRFC by 6 wickets at FB2.
Clint Irons scored 61 runs as JUBRFC closed their innings on 117 for 4.
Beeches reached their target with two balls to spare, Dave Buxton top-scoring on 51.
In three-over spells, James Perchard took two wickets for 26 runs for the winners and Irons three for 16 for the losers.
Tight bowling by St John’s Damien Maltwood, three overs nought for 11 and Rob English, three overs one wicket for 26 runs, restricted St Ouen to a five-over total of 28 for one off their powerplay.
Despite Paul Horton’s unbeaten 56, including three boundaries and three 6s, St Ouen never fully recovered from their moderate start.
Luke Gibson helped keep matters in check on his recent return from university with three wickets for 28 runs in his three-over spell holding St Ouen to 126 for 7 in their allotted 15 overs.
St John had a great start in reply as Rob Sanford hit 18 runs off the first over before being well caught by Robin Tewkesbury for a fine 36 including six boundaries.
John Evans played the anchor role to help guide St John home striking three fours to finish 36 not out.
Horton matched his batting performance with the ball taking three wickets for 19 runs in his three overs.
The final is scheduled for Thursday 19 July, at Grainville.
