The scope of this thesis is the evaluation of organic and natural materials as functional layers in organic field effect transistors (OFETs). Plant-based materials, like gum mastic, gum arabic, carnauba wax and cellulose are integrated as thin gate dielectrics layers, and indigo as thin semiconducting layer, in OFETs. Additionally, the non-natural organic material paraffin wax is used as gate dieletric and quinarcridone and pentacene are implemented as thin semiconducting layers. Before these materials (especially the dielectrics) are used in OFETs the surface and dielectric properties are investigated in detail. The surface properties are investigated by contact angle measurements, atomic force microscopy measurements and profilometry in order to determine the surface energy, RMS-roughness and the thicknesses of the thin films, respectively. In order to characterize the dielectric properties, capacitor structures with a bi-layer dielectric, consisting of alumina and a thin film of the new dielectric materials are fabricated. Furthermore, AFM measurements are done in order to characterize the morphology of the evaporated organic semiconductors films like pentacene, quinarcridone and indigo. An influence between the morphology of the semiconducting films and the electrical performance of the fabricated transistors is also observed. Many combinations of these materials showed excellent transistor behavior. Thin indigo films applied on paraffin wax even showed ambipolar transistor behavior. In this thesis, a new class of natural organic materials (in combination with non-natural organic materials) is successfully integrated as functional layers in OFETs and may contribute to a green, sustainable electronic future.