A high quality silicon-polyaniline heterojunction is produced by spin-coating of soluble polyaniline on silicon substrates. The devices have excellent reproducibility of their electrical characteristics and high rectification ratio. The rectification ratio is 60,000 at +/-1.0 V at room temperature, and typical reverse current at - 1.0 V is 3 nA. A G/I x G plot is used to analyze the current-voltage characteristics, yielding typical series resistance of 4 kOmega and ideality factor in a range from 1.0 to 2.0. The devices present great potential for use as radiation and/or gas sensors. (C) 2002 Elsevier Science B.V. All rights reserved.