This paper describes the process of development of a thin film thermal print head that provides 600dpi resolution.In order to achieve high definition printing using thermal transfer technology, it is essential for the print head to have fast thermal response, high thermal resistance and uniform contact pressure on print media. Subtle adjustment of the head is also required. With this point of view, we have evaluated a new structure and an optimum form for the print head.At first, we developed a thin film thermal head which has a new structure composed of a high-thermal-diffusion substrate made of single Si crystal and a low-thermal-diffusion layer formed through sputtering process. This permits the 600dpi thermal print head to be driven at high speed and print at high density.Secondly, we have succeeded in controlling edge distance, the distance from the center of heating elements to the edge of the head to approximately 130μm with tolerance of ±5μm or less by anisotropic chemical etching of the single Si crystal substrate. The optimum form of the specially developed print head allows resin ink to be stably transferred to plain paper. We call this print head Micro DOS (Deposition on Silicon) head.