We have succeeded in attaching deoxyribo nucleic acid (DNA) molecules to a semiconducting Si substrate by adding MgCl2 to the DNA solution. The optimum concentration of MgCl2 solution to form the DNA network structure is 0.05 to 0.5 mM@. Furthermore, it is found that DNA molecules attach to a hydrophilic SiO2 surface but not to a hydrophobic SiH surface. This result indicates that it is possible to fabricate micropatterning on a Si surface by using a DNA template and photolithography.