We developed a high-speed diamond synthesis technique called DIA-JET process that uses a DC plasma jet. Diamond is made by spraying the plasma jet (generated from the DC arc discharge) onto a water-cooled substrate. After examining the film with X-ray diffraction, Vickers hardness, and Raman scattering, we found that the quality approximated that of natural diamond. This paper describes the properties of the plasma jet and the synthesized diamond.