We have illustrated the effect of germanium doping in CZ silicon on mechanical strength, oxygen-related donors, oxygen precipitation and void defects. It has been established that the mechanical strength of silicon wafers could be improved by intended germanium doping, which benefits the improved production yield of wafers. It is also found that germanium suppresses the generation of TDs, which benefits the stable electrical property of wafers. More importantly, germanium has been found to suppress the formation of void defects, which can be annihilated easily during high temperature treatments. Moreover, oxygen precipitation can be enhanced by germanium doping, and therefore IG capability could be improved. Additionally, compared to nitrogen doped CZ silicon, germanium doping level in CZ silicon could be much easier to control, and no electrical Centers such as shallow thermal donors will be introduced. Ascribing to the novel properties, it is considered that GCZ silicon could satisfy the higher requirements of ULSI.