A method for calibrating a furnace enabling a semiconductor material to be subjected to a first thermal donor formation annealing that includes a temperature rise, a first temperature plateau and a temperature drop of the furnace, the method to including providing a calibration piece of the semiconductor material; determining the interstitial oxygen concentration of the piece; subjecting the piece to a second thermal donor formation annealing in the furnace, the second annealing including rise and drop in temperature of the furnace identical to those of the first annealing and a second plateau at the set temperature for a set time; determining the concentration of thermal donors formed in the piece during the second annealing; determining an equivalent annealing time at the set temperature, corresponding at least to the rise and drop in temperature of the furnace, from the interstitial oxygen concentration, the thermal donor concentration of the piece and the set time.