Abstract: The reliability of DC /DC power supply module-multichip module was investigated.By statistics the failure of modules applied and analysis the temperature distribution of the module used ANSYS software,it has found that the key devices affecting the reliability are VDMOS and SBD in the module.Then the VDMOS and SBD were tested under constant electrical stress and progressive temperature stress based on the parameter degradation.It concludes that the failure sensitive parameter are transconductance g_m for VDMOS and reverse current I_R for SBD,the average life span of VDMOS and SBD are 1.47 × 10⁷ hours and 4.3 × 10⁷ houres respectively from the extrapolation of accelerated life test curve.In conclusion,the degradation of VDMOS and SBD is dependent on the Na ⁺ contamination and Si-SiO₂ interface degradation.At same time,the degradation of SBD is also dependent on Al-Si interface degradation.