A method for producing a corrosion-, heat and oxidation-resistant material which comprises coating a substrate composed of at least one material selected from metals, carbonaceous substances and ceramics with a semi-inorganic compound, and heat-treating the coated substrate at a temperature of 300.degree. to 2000.degree. C. said semi-inorganic compound being a modified organoborosiloxane compound obtained by reacting an organoborosiloxane compound composed of (1) at least one siloxane unit selected from the group consisting of ##STR3## the content of the siloxane unit (C) being 0 to 30 mole% based on the total siloxane units, and (2) a boroxane unit of the formula ##STR4## with at least one organic compound selected from the group consisting of polyhydric aliphatic alcohols, aromatic alcohols, phenols and aromatic carboxylic acids at a temperature of from 250.degree. to 450.degree. in an atmosphere inert to the reaction.