FeCl3 is used as a dopant of organic semiconductors which have polyconjugated structures (e.g. polyacetylene, polyphenylene), as well as for the intercalation of graphite. Semiconducting polymers can be also synthesized by the pyrolytic conversion of organic polymers. The influence of FeCl3 as a dopant for pyrolysed aromatic polymers at different pyrolysis temperatures up to 1000 degrees C on their electrical conductivity, sigma, has been investigated. In the materials poly-p-phenylene, o, m, p-polyphenylenes, novolac resin cured with hexamethylenetetramine, biomass of olive stones, lignin Kraft isolated from this biomass, three regions can be distinguished. The electrical conductivity is low up to 500 degrees C, between 500 and 700 degrees C it increases greatly, and above 700 degrees C it increases at a lower rate. For o, m, p-polyphenylenes, these regions (especially the first and the second) cannot be distinguished. Similar curves are generally obtained after doping of the pyrolysed materials. The ratio of the electrical conductivity of doped, sigma to undoped, sigma(0), pyrolysed materials increases mainly between 500 and 700 degrees C with the exception of o, m, p-polyphenylenes, where the electrical conductivity decreases at all of the pyrolysis temperatures. The electrical conductivity of the materials is more strongly influenced by heating than by doping. The results are interpreted based on the structure of the materials using X-ray diffractograms, weight losses during the pyrolysis, and taking into consideration the reactions occurring during pyrolysis. FeCl3 is an effective dopant for organic semiconductors affected by charge transfer, but a less effective dopant for pyrolysed polymers and which do not lead to intercalation because of the low order and extension of the carbon layer formed in comparison to graphite.