A method for preparing ceramic material from a polymer which comprises selecting a polymer from the class consisting of poly(diorganosilanes), poly(haloorganosilanes), poly(carbosilanes), polysilazanes, polycarbocarboranes, and polyborazines; heating said polymer to a temperature from 700.degree. to 2000.degree. C at a rate of at most 100.degree. C/hr. in an inert atmosphere for at least one hour; and cooling to room temperature at a cooling rate which avoids thermal stresses.