Right-wing Sam Kingston helped himself to two of St Gerard's five tries as they qualified for a final showdown with Wesley College.
Left-wing Adam Simmonds, replacement forward Charlie Kenny and the flying Kingston (two) got in on the try-scoring act, as St Gerard's moved into an unassailable 24-0 lead.
Mount Temple simply could not cope with the pressure.
They were in constant retreat from the kick-off, with prop Aaron Jackson-Ryan scrummaging heroically to stem the tide and No 8 Sam Gibney leading the pack towards the team's only score.
That came from the boot of fly-half Daragh Irwin when he landed a second-half penalty.
However, there was still time remaining for outside-centre Con Callan to roll out the final try in this one-sided clash.
Victory here also means St Gerard's have earned the right to play Clongowes Wood in the first round of the Senior Cup next Thursday.
St Gerard's – M Prendergast; S Kingston, C Callan (R O Caoimh 59), C Jordan, A Simmonds (M Gallagher 44); T Whittle, D Baker (S Murray 60); N Buckley (N Byrne 44), J Ryan, T Kenna, H Conan, M Loughman (C Kenny 4), B Fitzpatrick (S Tyrell 40), D King (A Symes 51), F Smith (capt).
Mount Temple – E Prior; A Lynch (G Dunne 65), D Gill, D O'Byrne, S Jennings (B Warren h-t); D Irwin, T Beechinor; A Jackson-Ryan, S Reamsbottom, C Kelly (L Scullion 25, L Kearney 65), G Keogh, J Bethal, R Shaw (J Dawson 59), R McCann (N Broaders 59), S Gibney.
REF – M Scoyne (Leinster Branch).