A detailed study of the effects of the time-dependent or aging on the characteristic parameters of polypyrrole/p-type Si/Al structure has been presented. The polypyrrole film has been formed on a p-type Si substrate by means of an anodization process. The polypyrrole/p-Si contact has demonstrated clearly rectifying behavior by the current-voltage curves studied at room temperature. The current-voltage (I-V) curves of the diode have been measured immediately, 7, 15, 30, 60 and 90 days after fabrication of the polypyrrole/p-Si contact. It has been seen that the characteristics parameters such as barrier height, ideality factor and series resistance of polypyrrole/p-type Si/Al structure have changed with increasing ageing time. Furthermore, the density distribution of interface states of the device was obtained from the forward bias I-V characteristics. The fact that the diode shows non-ideal I-V behavior with increasing ageing time may be ascribed to a slow replacement of the initial doping agent by oxygen and this process certainly plays a role in the aging of the diode. (C) 2004 Elsevier Ltd. All rights reserved.