AbstractSemiconduction and electron spin resonance studies on a number of conjugated polymers representative of the polyacetylenes, the polybenzimidazoles, and the polyacene quinone radical polymers were made. Observed resistivities ranged from 270 to 1016 ohm‐cm. at room temperature. These and the spin concentrations, the relaxation times, and the energies of activation of conductance and spin concentration were found to be functions of the molecular structure. It was considered impressive evidence that impurity effects on the electronic properties of molecular solids are far less than those commonly observed with the covalently bonded semiconductors such as Ge and Si, for example. A detailed analysis was made of the carrier and free radical formation and life‐times in these ekaconjugated molecular solids using a simple model.