The knowledge about properties of electronic traps in organic semiconductors is one of the major keys for the understanding and optimization of charge transport in organic devices. In the present article the density of occupied states of the most prominent pristine small molecule systems and selected polymers are reported determined, by fractional thermally stimulated current and luminescence techniques. In order to distinguish between impurity and structurally based traps, model systems of doped as well as differently deposited layers were studied. In addition, the influence of detected traps on steady state I–V and dynamic time-of-flight characteristics are reported. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)