Midfielder Ibrahim Afellay and strikers Nyron Wau - currently on loan at Helmond Sport - and Otman Bakkal have all signed three-year deals.
PSV are also considering whether to exercise their option of a two-year deal for young Belgian Sep de Roover.
The Dutch giants have also extended the loan of Robin Faber to De Graafschap for a further year.
Youngster Leon Hese has arrived back at the club from Helmond Sport as he recovers from a knee ligament injury.
