By referring to the theories of thermoelasticity and thermal interlaminar stress of composite, the stress in silicon wafer and the interlaminar stress of structure Si/Al/Mo used for making thyristor after sintering were analyzed. It was found that the distribution of stress caused by different properties of thermal expansion in the center portion is different from that at the edge of silicon wafer. The expression for stress at the edge of silicon wafer was derived. The stress photoelastic patterns were obtained by means of the infrared photoelastic system. The theory coincides well with the results of experiment.