This work reports the influence of nitridation on structural and electrical properties of La2O3 gate dielectric films. The issue of La2O3 is EOT increase after high temperature post metarization annealing (PMA). To overcome this problem, we incorporated nitrogen in La2O3. The EOT increase on the TaN/LaON and W/LaON structure is reduced compared with that on the W/La2O3 structure. This is due to nitrogen in LaON and SiNx-rich interfacial layer which seems to remain after high temperature annealing. W/LaON nMOSFET is also successfully fabricated. Peak electron mobility of 96.2 cm2/V s was obtained.