Christian Bassagog scored late in stoppage time to add to Ngadeu-Ngadjui 71st minute opener as the Indomitable Lions reach their first final since 2008.
Ngadeu-Ngadjui broke the deadlock late in the second half after the Ghanian defence failed to clear out a loose ball.
Razak came off his line to intercept a freekick delivered from outside the area but got nowhere near the ball which fell to Ngadeu-Ngadjui, who cooly placed the ball to the roof of the net.
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Ghana failed to turn on the pressure on their West African neighbours, as they could not capitalize on dreadful crosses into the Camerounian box.
The Black Stars were punished for their scruffiness in stoppage time when Aboubakar played in Bassagog, who carried the ball forward 30 yards and flipped it past Razak to finish off a wonderful counter attack.
The Indomitable Lions will play Egypt in Sunday’s final, while Ghana will slug it out with Burkina Faso for a third place finish.