Electrochemically polymerized polypyrrole (PPy), using tetraethylammonium toluenesulfonate (TOS), nickel phthalocyanine toluenesulfonate (NiPcTS), or copper phthalocyanine toluenesulfonate (CuPcTS) as dopants, forms a conducting organic polymer. The electrical properties of a gold contact to these doped PPy-layers (Au/PPy) were evaluated by current-voltage characteristics and capacitance-voltage measurements. The I-V characteristics of these junctions are asymmetrical and nonlinear. The junction parameters, as the ideality and the rectification factor, are strongly influenced by the dopant of the conducting polymer. In both forward bias and reverse bias, these junctions exhibit a significant, fast and reversible response to NOx gas, which was explained by changes in the Schottky barrier height and in the carrier concentration of the PPy layer due to NOx exposure. A simultaneous compensatory effect of NOx gas of the barrier region and of the neutral bulk of the Au/PPy-CuPcTS junction with a PPy layer thickness of 1.8 mu m was observed and confirmed by C-V characteristics.