The potential application of molecular organic semiconductor needs the control adjustment of conductivity. The hole transport materials (HTL) alpha-NPD (N,N'-di(1-naphthyl)-N,N'-diphenylbenzidin) has been doped with metal oxide (molybdenum oxide) for the study of transport phenomena. Impedance spectroscopic measurements were performed with the applied external electric filed. The activation energy calculated (0.55, 0.48 and 0.50 eV) decreases with doping of metal oxide. There is a clear indication of space charge limited (SCL) conduction in the doped and undoped thin films. The cole-cole plot indicates the device can be represented by a parallel resistance and capacitance network in series with a series resistance (of 70 Q). At high frequency; the conduction follows the universal power law for both doped-undoped alpha-NPD with MoO(3) and the onset frequency increases with increasing bias voltages. The conduction mechanism can be explained by classical hopping barriers (CHB) mechanism for the system. (C) 2008 Elsevier B.V. All rights reserved.