Abstract A radio frequency (RF) driven negative ion source has been designed for the ITER neutral beam injectors, as an alternative to the traditional arc driven solution. The main advantage of this technology is to avoid the presence of the filaments, that require periodic maintenance and consequently frequent shutdowns. The requirements for the ion source of the ITER NBI are to provide a uniform flux of D−/H− to the plasma grid of the accelerator that will result in a beam current of 40 A at 1 MeV. The present specification is for a filling pressure of 0.3 Pa. The ion source needs to provide 20/28 mA/cm2 D−/H− current density across the 0.58 m × 1.54 m aperture array for 3600 s. The source, consisting of a main chamber facing the plasma grid, of eight RF drivers and the auxiliary systems for power transfer, cooling and diagnostic purposes, is housed in the same quasi-cylindrical structure that supports the arc driven solution. Specific electric and hydraulic circuits have been designed and verified. In the paper the analyses performed for the design of the components are presented in detail.