Neath beat Aberavon 27-22 in their Swalec Cup semi-final to earn a final against Pontypridd at the Millennium Stadium on Saturday, 4 May.
Gareth Gravell (2) and Dafydd Howells scored Neath tries at St Helen's with Matthew Jenkins replying.
Pontypridd reached their third successive final with an 18-16 win over Carmarthen Quins at Aberavon.
Dan Godfrey and Huw Dowden crossed for Ponty, while Alex Pickersgill and James Dixon scored Quins tries
Pontypridd lost the 2012 final 32-19 to Cross Keys and last won the Cup when they beat Aberavon 35-24 at the Millennium Stadium in 2011.
Neath last won the Cup in 2009, beating Llanelli 27-21.