We investigated Gd 2 O 3 and Zr-incorporated Gd 2 O 3 films grown on Si (100) as a function of nitridation temperature under an NH 3 ambient and the incorporation of Zr into the film. The formation of a silicide layer at the interfacial region was suppressed in cases of Zr-incorporated or NH 3 -nitried Gd 2 O 3 films. The crystalline structure was affected when zirconium, with a relatively small ionic radius, was substituted with gadolinium. When the concentration of Zr atoms in a Gd 2 O 3 film reaches a specific level (Gd 0.6 Zr 1.9 O 4.3 ), phase transition occurred from cubic Gd 2 O 3 to monoclinic ZrO 2 . However, the monoclinic phase disappeared after nitridation at 900°C in an NH 3 ambient. The majority of the nitrogen atoms accumulated near the interface in the films and the concentration of incorporated N increased with increasing Zr content and NH 3 annealing temperature. Moreover, nitrogen atoms bonded to Zr-silicate at the interface, in preference to ZrO 2 in the film. These incorporation characteristics of nitrogen into Zr-incorporated Gd 2 O 3 film have an effect on the thermal stability and crystalline structure of a film.