The emission spectra of STM‐induced luminescence for Au(111) with Pt‐Ir alloy have been studied. We have observed the STM‐tip dependent emission spectra. The emission spectra with Pt‐Ir(20&percent;) tip are not well reproduced, showing various spectra depending on the nature of the tip apex, while the spectra with pure Pt or Pt‐Ir(10&percent;) tips are reproducibly obtained. The STM‐induced emission spectra for different STM tips have been calculated by the electromagnetic theory with complex dielectric functions defined in two different ways for alloy material, and compared with the experimental results. The characteristics of the spectra are interpreted in terms of the one mode type and two mode type depending on the composition rates. © 2003 American Institute of Physics