The SIK beta X-ray emission spectra for several silicates and silico-phosphates were measured using a high-resolution X-ray fluorescence spectrometer with two InSb(III) analyser crystals. Molecular orbital calculation analysis for the obtained spectra was performed by a SCC-DV-X alpha method and the energy positions and relative intensities of the spectral fine structures were calculated with Slater’s transition-state method. The calculated results interpreted the spectral profiles successfully. The energy shifts of the SiK beta main peak were also discussed in terms of the electronegativity of the second-nearest-neighbour atoms. These shifts were attributed to the changes in the stability of the Si-O bonds due to the existence of second-nearest-neighbour P atoms.