An instrument for analysing the composition of semiconductor material below the surface, using X-rays emitted by the material in response to stimulation by a beam of electrons. The instrumentation is essentially a scanning electron microscope (SEM) combined with an X-ray fluorescence detector. The X-ray detector is mounted on a normal SEM and the electron beam of the SEM excites atoms in the material. Both the normal SEM picture and the X-ray spectra are produced simultaneously. The energy dispersive spectroscope (EDS) is a sensitive X-ray detector that detects all wavelengths simultaneously. The method is not very sensitive to low atomic number elements, which tend to emit Auger electrons rather than X-rays.

X-ray fluorescence (XRF) is a very similar technique but an X-ray beam is used to produce the X-ray output rather than an electron beam. XRF produces poor lateral resolution because of the lack of focusing of the X-ray beam but it does have very good sensitivity. Once again low atomic number elements are not detected because of the emission of Auger electrons rather than X-rays.