Neath only just scraped through to the semis after sneaking home 32-31 against a fired up Cross Keys in the quarter-finals while Llanelli had to fight hard to repel Glamorgan Wanderers 27-20 at Parc y Scarlets.
Swansea brushed aside Caerphilly 62-3 but Aberavon had to work considerably harder to beat Newport 20-10.
Llanelli head of rugby Anthony Buchanan is expecting a tough challenge from Aberavon.
"It's going to be quite a challenge and we look forward to that," he said immediately after the draw. "It should be an interesting contest because we feel at the moment we are very fortunate to be in the next round as we didn't play well against Glamorgan Wanderers. But we're in the hat."
The draw for the Swalec Plate and Bowl will be revealed on www.wru.co.uk on Monday.