Highly conducting polyanilines (PANI) with thermal stabilities superior to that of polyaniline doped with hydrochloric acid (PANI-HCl) have been prepared by postsynthesis treatment of the PANI-base with three different phosphonic acids, R-PA, where R = butyl (Bu), decyl (Dc), and benzyl (Bn). X-ray photoelectron spectroscopy (XPS) results indicate the occurrence of free dopant molecules in the sample matrix, partial segregation of dopant species to the polymer surface, and participation of H3O+ as counter charges to some of the dopant anions in these samples. Infrared (IR) data suggest minimal perturbation of the PANI vibrational states when Cl- is replaced by RPO2(OH)-. Isothermal studies show the vastly superior thermal stabilities of the PANI-RPA over those of PANI-HCl. Thermogravimetric analysis has demonstrated a condensation reaction above 150-degrees-C among the POH and NH functions to give a cross-linked structure with loss of electrical conductivity. The stepwise doping process of PANI-base by different amounts of BnPA was followed closely by ultraviolet-visible spectroscopy (UV-vis).