The Serie A side have announced the capture of the Algeria international, while the Colombian wing-back has moved on
The left-back had long been linked with a move to the Serie A side and has now signed a four-and-a-half year deal with the Partenopei.
Ghoulam, 22, came through the ranks of the Saint-Etienne youth academy and made his official first team debut in September 2010.
The defender has since made close to 100 official appearances in all competitions for ASSE, earning himself a move to Serie A with his fine performances this term.
Ghoulam becomes Napoli's fourth signing of the January transfer window after the previous arrival of Jorginho, Henrique and Mariano Andujar.
Meanwhile, Napoli have sent out Colombian wing-back Pablo Armero out on loan to West Ham until the end of the season.
The 27-year-old joined Napoli from Udinese in January 2013, but moves to Upton Park in a bid to boost his chances of making Colombia's World Cup squad, with his appearances limited in Naples.