The clubs join SWALEC Cup finalists Pontypridd and Aberavon who beat Swansea and Llandovery on the weekend to claim their place at the showpiece event in Welsh club rugby.
Ammanford are on course for a second SWALEC Plate title in three years after a convincing 58-26 defeat of Division Three West’s Gorseinon.
They beat Risca 46-20 in 2009, buoyed by a large travelling support and will return for more of the same in three weeks’ time.
Centre Tom Rees was the star of the show in the semi after his four tries sent the SWALEC Division Two West outfit into the final. There were two apiece for wing Mike Evans and No 8 Richard Davies while flanker Johnny Evans also went over.
John Ogden added four conversions and Dean Bromham kicked a conversion and a penalty.
The Cherry and Whites battled hard to remain in contention at half-time, trailing 20-14, before Rees eased Ammanford to a comfortable victory.
Glynneath hosted that semi-final but were celebrating their own success after a shock victory over Tondu.
Dale Newell crossed for the only try of the game as third division outfit Glynneath toppled Tondu, of Division Two, 16-3 at Morriston.
The kicking of Jack O’Reilly also proved crucial, adding the conversion as well as two penalties and a drop goal. Dean Thomas landed Tondu’s only points.
SWALEC Plate Semi-final results
Gorseinon 26 Ammanford 58 (Glynneath RFC)
Tondu 3 Glynneath 16 (Morriston RFC)
SWALEC Plate Final to take place at Millennium Stadium on Monday, 2 May (3.15pm).
Tickets for the SWALEC Finals Day are £10 for adults, £5 for Under 16s, OAPs and SWALEC customers*, available from Ticketmaster tel 08442 777888 and www.ticketmaster.co.uk, from the Cardiff Arms cafe/store, No 8 Westgate Street and from all participating clubs
*SWALEC customers can gain their discount code from swalec.co.uk/rugby
