Application of high pressure and high temperature has been used to synthesize a new compound: boron monosulfide. Two polymorphs have been made by varying the temperature. A cubic phase was formed at 60 kilobars pressure and 1500° C., and an orthorhombic phase was formed at 60 kilobars and 1400° C. The synthesis procedure has been optimized and the best results were obtained at these conditions using water as a mineralizer. Without the water, it is necessary to use higher temperatures to form the cubic phase. The cubic material is very stable at atmospheric conditions and does not react with common acids or bases. Its density was measured to be 2.52 gm/cm 3 in the powder form with some of the larger crystals measuring at 2.58 gm/cm^3 It is a light olive color in the powder form and the larger crystals are transparent with a deep yellow color. The orthorhombic material is a light tan color and its density was measured to be 2.53 gm/cm^3. The crystal systems of the two polymorphs were determined by X-ray diffraction. It was not possible to determine the space group to which the cubic system belongs due to the imperfections in the crystals. Attempts to grow single crystals large enough to analyze properly by single crystal diffraction were not successful. The crystallite size was determined roughly by line broadening of the X-ray diffraction pattern to be 120 A. in the cubic material. The cell parameter, as measured from the X-ray diffraction pattern, was found to be 4.39 A.