The holders will face Builth Wells at Lampeter, with the winners going on to play either Glynneath or Pontypool United, who clash in the other semi at Tata Steel RFC.
LLandeilo extended their unbeaten run last season to 18 games with their 22-19 Principality Stadium victory over Tonmawr in a gripping final. Five of the starting XV from the 2024 final, Sion Jones, Ioan Thomas, Llyr James, Gruff Jones, Rhodri Jenkins, are still in the line-up, along with Lloyd Thomas, Michael McDonagh, Ryan Sargeant and Iwan Blakeman, who were all on the bench.
Toby Trickett has been succeeded as captain by Rhodri Jenkins and they have Scarlets U18 full back Sion Jones as one of their stand-out players.
Builth Wells have reached the final on the back of wins over Rhyl & District (43-7) and Aberdare (22-15. They were last in the final I 2022, when they beat Bridgend Athletic 44-17.
In the other semi-final, Glynneath triumphed 38-12 at home against Tondu and then won 24-19 at Blackwood and 18-13 against Carmarthen Athletic at home to reach the final four. Pontypool United have beaten Bargoed (44-0), Pencoed (37-21) and Merthyr (18-3) to reach this stage.
Reps: WRU U18 Clubs Cup Semi-Finals (2.30pm)
Glynneath v Pontypool United (Tata Steel RFC), Llandeilo v Builth Wells (Lampeter RFC)
WRU U18 Clubs Plate Semi-Finals (2.30pm)
Haverfordwest v Barry (Trimsaran RFC), Gorseinon v Crymych (Nantgaredig RFC)
WRU U18 Clubs Bowl Semi-Finals (2.30pm)
Abercwmboi v Llanishen (Senghenydd RFC), Cardiff Quins v Aberystwyth (Tenby United RFC)
WRU U18 Clubs Shield Semi-Finals (2.30pm)
Abercynon v Abergele (Llandrindo Wells RFC), Llantrisant v Felinfoel (Tumble RFC)
