Doping of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) with antimony pentachloride (SbCl5) as a method to form its p-type organic semiconductor material is described. UV-visible absorption and X-ray photoelectron spectroscopic (XPS) data indicated formation of radial cations and dications in TPD films doped with SbCl5. This doping played important roles in hole conduction and in hole injection from an indium-tin oxide (ITO) electrode to the doped TPD layer in typical electroluminescent (EL) organic thin film devices.