The capacitancevoltage (CV) measurements of GaNbased Schottky diodes were carried out in the frequency range of 0.3～1.5MHz. Anomalous peaks and negative value of capacitance were observed in the CV plots of Au/iGaN Schottky diodes under forward bias, while neither of them was seen in the plots of Au/iAl0.45Ga0.55N Schottky diodes. Based on the parameters extracted from the currentvoltage (IV) and CV plots of GaN and Al0.45Ga0.55N Schottky diodes, the peak and negative capacitance are ascribed to the capture and loss of interface charges. These processes are greatly suppressed when there exists a huge series resistance in the diode.