Penallta RFC will face local rivals Bedlinog RFC in the final of the SWALEC Plate at the Principality Stadium on Sunday May 1.
The Ystrad Mynach side booked their place in the final with a 24-21 win over Skewen on Saturday April 16.
Back-rower Rhys Fitzgerald scored to give Penallta an early lead, before two further tries from centre Andrew Jenkins sent them into the break 21-3 up.
However, Skewen were relentless in their comeback efforts in the second half, and with the scores level at 21-21, Penallta outside-half Matthew Brewer kept a cool head to slot a late penalty and give his side a shot at silverware.
The final sees Penallta face their Division One East title rivals, Bedlinog, after they beat Cwmllynfell 38-10.