the key processes of silicon-wafer direct bonding (sdb), including hydrophilic surface formation and optimal two-step heat treatment, have been developed. however, h/sub 2/so/sub 4//h/sub 2/o/sub 2/ solution being a strong oxidized acid solution, native oxide is found to have grown on the wafer surface as soon as a wafer is treated in this solution. in the case of a wafer further treated in diluted hf solution after hydrophilic surface formation, it is shown that the wafer surface can not only be cleaned of its native oxide but also remains hydrophilic, and can provide excellent voidless bonding. the n/sup +//p and n/p combination junction mesa diodes fabricated on the wafers prepared by these novel sdb technologies are examined. the ideality factor n of the n/p mesa diode is 2.4 approximately 2.8 for the voltage range 0.2 approximately 0.3 v: hence, the lowering of the ideality factor n is evidently achieved. as for the n/sup +//p mesa diode, the ideality factor n shows a value of 1.10 approximately 1.30 for the voltage range 0.2 approximately 0.6 v: the low value of n is attributed to an autodoping phenomenon which has caused the junction interface to form in the p-silicon bulk. however, the fact that sustaining voltage of the n/p mesa diode showed a value greater than 520 v reveals the effectiveness of this novel sdb process