This study examines the intensity drops (‘negative peak’, ‘hole’, or ‘background hole’) in the X–ray spectra of a wavelength–dispersive spectrometer with a pentaerythritol (PET) analyzing crystal. The PET crystal in the (002) orientation has a total of thirty three possible hole locations in the range 25° < 2θ < 125°. Eight of these were observed experimentally at 2θ = 31.053°, 31.262°, 38.302°, 38.937°, 43.493°, 45.264°, 59.161°, and 69.564° using an electron probe microanalyzer. It is important to ascertain the background intensity profile around each hole by wavelength scanning on a given spectrometer because, like the characteristic peaks, the shape and magnitude of holes depend on the specific spectrometer characteristics.