One problem encounted when using the hydrogen annealing process is plastic deformation (slip) of the silicon wafers during heating, in particular, with 300 mm wafers where annealing is carried out at high temperature (1200 degrees C). The reduction of stress due to gravitational effects in wafers with large diameters were investigated with particular emphasis on the configurations used for horizontally holding the wafers. We theoretically found(1) that moving the position of the supporting points normally located at the periphery of the wafers to the inner position significantly reduced the gravity-induced stress (b/R = 0.55 and 0.7). Experimental results were in agreement with our theoretical predictions.