In this study, the characteristic physicochemical and electrical properties of HCl‐doped polyaniline (PAni) films grown via oxidative chemical polymerization of aniline on n ‐Si(100) are presented. Two exothermic processes were found for 0.2 M HCl solution during aniline polymerization while all others underwent one exothermic process only. All polyaniline films were of emeraldine salt form that exhibited connected rod‐like to agglomerated grains and dendritic surface morphologies on top of wetting layer with increasing hydrochloric acid concentration. Rectifying behaviour of p‐ PAni/n ‐Si(100) heterojunctions were also found indicating the formation of p‐n junction between p ‐PAni and n ‐Si(100). (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)