Diamond has attracted considerable attention as a next-generation high-temperature and radiation-proof semiconductor material, which can be applied in extremely harsh environments, such as in space or nuclear energy industry. To realize intelligent systems with diamondbased integrated circuits, not only transistors but also passive components (e.g., resistors, capacitors, and inductors) are required. In this study, we prepared heavily boron-doped (p+) diamond resistors via selective area growth by hot-filament chemical vapor deposition. Finger-shaped p+ patterns of various sizes were fabricated. By designing the shape and film resistivity, we demonstrated that p+ resistance could be well controlled. A small temperature-dependence of the resistance was confirmed. This is a characteristic of heavily B-doped diamond possessing a low activation energy. The resistance remained unchanged under 500 kGy X-ray irradiation, confirming the radiation hardness. These results will support the development of radiation hardened diamond-based electrical components.