The correlation of the corrosion behaviour and semiconductor characteristics of a passive film on Incoloy 825 in 5%~30% NH4Cl solutions was investigated using potentiodynamic polarization scan, Mott-Schottky curves，scanning electron microscope(SEM) and the point defect model(PDM).The results indicate that Incoloy 825 is self-passivated and has a pitting tendency in all four concentrations of NH4Cl solution at 50°C. With the increasing NH4Cl solution concentration, the quantities of chloride ions absorbed in passive films on Incoloy 825 increase, which can increase the quantities of cation vacancies for the Mott-Schottky reaction, so the quantities of point defects in the passive film on Incoloy 825 increase and the anodic dissolution and pitting of Incoloy 825 becomes easier. Therefore, the passive current density of Incoloy 825 increases, and the pitting potential of Incoloy 825 shifts negatively with the increasing concentration of ammonium chloride.