This paper presents and compares the results of investigation of the samples in the Bi₂O₃-P₂O₅-SiO₂ system by means of simultaneous thermal analysis, X-ray phase analysis, and Knudsen effusion mass spectrometry. The samples were synthesized by the melt quenching technique using Bi₂O₃, SiO₂, and NH₄H₂PO₄. By differential scanning calorimetry, characteristic temperatures and enthalpies of phase transformations in the samples were determined. Mass losses of the samples obtained by thermogravimetric analysis in dynamic air flow were compared with those found by Knudsen effusion mass spectrometry in vacuum. Using X-ray phase analysis, unknown phases were identified in several samples. These phases might consist of previously unknown compounds containing bismuth, phosphorus, and silicon together. The results of the present study should be regarded as being preliminary information concerning phase equilibria in the Bi₂O₃-P₂O₅-SiO₂ system.