TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred High-purity Si: The solid SiO is preferably heated to a temperature higher that the melting point of Si but not more than 1730degreesC, followed by separating the generated liquid Si form the solid SiO and/or SiO2. The heating of solid SiO may also be conducted at not less than 1000degreesC but below the melting point of Si by heating and maintaining before heating at a temperature above melting point of Si but not more than 1730degreesC. The disproportionation reaction is performed when the molar ration of Si to SiO2 is 1:x and under the conditions that can satisfy 1.5 +/- x +/- 0.5. During such disproportionation, the reaction system is practically sealed without supplying fresh atmospheric gas to prevent vaporization of SiO; with controlled atmospheric gas supply, the Si to SiO2 molar ratio of 1:x is then realized, and particularly the above atmospheric gas contains oxidative or reductive gas with control of Si to SiO2 molar ratio at 1:x. Average particle diameter of the solid SiO2 is 1 mum to 5 mm, in granular shape. Amount of impurity in the generated Si is not more than 1/10 of that in the solid SiO; particularly there are reduced amounts of phosphorus and boron impurities in the generated Si as compared with those in the solid SiO. The obtained Si is purified by solidification to a high degree of purity. The solid SiO is produced by heating a mixture of 1 or more chosen from carbon (C), Si and ferrosilicon with SiO2 to generate a gas containing SiO prior to cooling to form solid SiO. During cooling the gas containing SiO, impurity is removed at a first temperature above the initial solid SiO precipitation temperature in the first zone, then a second temperature at 30degreesC above the solid SiO precipitation temperature is operated in the second zone and the precipitated SiO in this second zone is used as starter in the disproportionation reaction. A SiO-containing gas is cooled in a reactor with a temperature gradient from high to low by supplying the gas from the high temperature side. The impurity in the solid SiO is only 1/100 of that in the starting C, Si or/and ferrosilicon and SiO2; particularly phosphorus amounts in C, S and ferrosilicon as well as SiO2 are not more than 1 ppm. During rapid cooling of the SiO-containing gas, the solid SiO is produced in granular form. Preferred Production Equipment: The equipment contains a part for cooling SiO-containing gas which includes a device for cooling with heat-insulation and expansion, SiO solid precipitation region where a temperature of not less than 300degreesC can be maintained, a region where impurities can be removed, exhaust gas remover e.g. gas after precipitating SiO, a powder recovery device to recover the powdery SiO, and a heat-treatment vessel in the thermal decomposition region at the bottom of which is an extraction aperture for removing melted Si and also a plurality of heaters, particularly expanded into a zone, for individual heating if needed with a mechanism to transfer the solid SiO between the heating region. EXAMPLE - Into a quartz ball vessel (40 mm outer diameter; 5 mm thick) was charged with solid SiO (99.999% pure; particle diameter 0.1 mum; 20 g) and vacuum-sealed at room temperature then heated with infrared to 1500degreesC rising at 80degreesC/hr. to produce 6.3 g spherical pieces of Si with metallic shine of diameter 5-10 mm (99.9999% pure), when operated with Si to SiO2 molar ratio of 1:x where x = 1.005. By elemental analysis of the generated Si: Al = 0.05 ppm, B = 0.1 ppm and P = 0.1 pp; in the other non-Si pieces, Al = 1.45 ppm, B = 1.42 ppm and P = 0.1 ppm.