Guinean striker Naby Laye Keita scored in the second minute to put the Porcupines in the lead but goals from Yussif Mubarik, Emmanuel Owusu and Mark Agyekum turned the game around for The Miners at the Accra Sports Stadium.
The Porcupines' defeat comes three days after a famous penalty shootout win over arch-rivals Hearts of Oak in the tier one championship.
In the final, Ashgold will face Nzema Kotoko who beat UniStar Academy 2-1 in the second semi-final.
Unistar broke the deadlock through Ali Muftawu in the 26th minute but Francis Atitsogbe restored parity three minutes later before Agyenim Boateng slotted in a penalty on the stroke of half-time to seal a comeback win.
The final is billed for June 30 with the winners set to represent Ghana in the Caf Confederation Cup next season.