Semiconducting and metallic “organic” polymers are based on sp2 hybridized linear carbon chains. When charge carriers (from the addition or removal of electrons) are introduced into the conduction or valence bands (see below) the electrical conductivity increases dramatically. The most notable difference between conductive polymers and inorganic semiconductors is the mobility, which until very recently was dramatically lower in conductive polymers than their inorganic counterparts, though recent advancements in molecular self-assembly are closing that gap.
Typically "doping" the conductive polymers involves actually oxidizing/reducing of the compound. Conductive organic polymers associated with a protic solvent may also be "self-doped". Melanin is the classic example of both types of doping, being both an oxidized polyacetylene and likewise commonly being hydrated. The conjugated polymers in their undoped, pristine state are semiconductors/insulators.