The invention provides a novel method for providing the surface of various kinds of substrate articles, e.g. sapphire, quartz, alumina, metals, glass, plastics and the like with a coating layer of an amorphous silicon carbide of the formula Si.sub.x C.sub.1-x, in which x is a positive number of 0.2 to 0.9, by exposing the surface of the substrate article to an atmosphere of plasma generated in a gaseous atmosphere of an organosilicon compound having no halogen or oxygen atom directly bonded to the silicon atom, such as hexamethyl disilane, optionally admixed with a vapor or gas of a hydrocarbon compound, e.g. methane, benzene and the like.