The electric field controlled bulk-like optical second-order susceptibility&khgr;(2)in thicker(Si5Ge5)100superlattices is reported. The relation between&khgr;(2)and the broken structural symmetry by applied external field was observed. The measured large value of&khgr;(2)for(Si5Ge5)100superlattices is evaluated to be∼5×10−6esu with the external field of 100 kV/cm, which indicates that(Si5Ge5)100superlattices have potential applications in optoelectronic devices. ©1997 American Institute of Physics.