Various organic conjugated materials, e.g. conjugated polymers and short conjugated oligomers, have been up to now proposed as active semiconducting layers in organic-base devices, such as thin film transistors, TFTs, or light emitting diodes. The mode of operation of TFTs shows that a high carrier mobility together with a low conductivity are required for their figure of merit. Experimental results from literature indicate that, whereas conjugated polymers exhibit a low carrier mobility, of the order of 10-4 to 10-5 cm2V-1s-1, conjugated oligomers appear much more promising. It is thus shown that carrier mobility is directly related to the long range structural order in conjugated oligomer films, i.e. to the decrease of grain boundaries, leading to values of the order of 10-1 cm-2V-1s-1, comparable to that of amorphous hydrogenated silicon. Conjugated oligomers are well defined materials, offering various physical and chemical ways for control of the structural organization of thin films made from them. Besides, conductivity in thin films of conjugated oligomers is mainly determined by the purity of the materials, allowing values lower than 10-7 Scm-1, with a high on/off ratio. The low melting and evaporation temperatures of conjugated oligomers, together with the solubility of some of these materials, allows the construction of TFTs by the use of room temperature techniques, following a process compatible with paper technology.