We have developed a new experimental method of X-ray photoemission spectroscopy (XPS) that can map out the core-energy levels as a function of depth from the surface of the film. A series of XPS data are recorded with different detection angles and expanded to the Taylor series of angle-averaged spectra using the target factor analysis. This procedure enables conversion of the measured angle variations in XPS to the core energy levels as a function of depth from the surface. This method has been applied to profiling the electronic levels of buried interface between organic semiconductor and metal surfaces. (C) 2011 Elsevier B. V. All rights reserved.