The highest density DNA chip reported to date was developed using a DNA solidification technique for vertical binding to the surface of a chemical vapor deposition (CVD) diamond chip. The covalently bound oligonucleotide was approximately 42 pmol (∼2.5×10 13 molecules) per 9 mm 2 of chip surface. Using the oligonucleotide as a linker, large DNA molecules (21 kbp fragment from λ-phage DNA) were covalently bound in the amount of approximately 2.6 fmol (∼1.6×10 9 molecules) per 9 mm 2 of chip surface. To test the potential of the technique for repeated utilization of one piece of the DNA chip, PCR enhancement of a 500 bp region within the 21 kbp λ-DNA fragment was applied over 50 times. The results suggest that a diamond DNA chip is excellent for the preservation of limited and/or valuable gene samples. Furthermore, the technique of high density DNA solidification to a CVD diamond chip will be useful for DNA diagnosis in the future.