A metallic polypyrrole film has been directly formed on a p-type Si substrate by means of an anodization method under conditions of constant current density by an electrolyte being held at a constant temperature of 55 degrees C that was composed of 0.40M pyrrole and 0.10M tetrabutylammonium tetrafluoroborate. An aluminum electrode was used as an ohmic contact. The polypyrrole/p-Si/Al structure has clearly demonstrated rectifying behavior by the current-voltage curves studied at room temperature. The capacitance-voltage-frequency curves of the structure have been measured at different frequencies at room temperature in dark. To observe the effect of the aging, the measurements were also repeated 7, 15, 30, 60, and 90 days after fabrication of the polypyrrole/p-Si/Al Schottky diode. During the whole measurement process, the probe of holder on sample was fixed to eliminate effects of surface inhomogeneity. The interface state density distribution curves of device have been obtained from forward bias current-voltage (I-V) and cap acitance-frequency (C-f) characteristics as a function of aging time. From these curves, the exponential growth of the interface-state density from midgap toward the top of the valence band is very apparent. The shape of the interface state density distribution curves from the forward bias I-V characteristics are very similar to those obtained from C-f. (c) 2006 Wiley Periodicals, Inc.