The influence of surface states on photoelectron emission phenomena was investigated to determine the work function precisely. A new method for analyzing the yield spectra of photoelectron emission as a function of temperature has been developed. This method was used to decide the work function and surface state of aluminum metal sheets mechanically scratched and ultrasonically cleaned in organic solvent. The yield spectrum as a function of photon energy exhibited a greatly changed shape with an increase and subsequent decrease in temperature in flowing Q gas under the irradiation of 220 nm wavelength light. The ionization energy of a surface state generated at the surface by the influence of temperature and light was estimated. [DOI: 10.1380/ejssnt.2005.179]