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• High-density hydrogen generator was developed for unmanned aerial vehicles. • Solid-state NaBH 4 was used as a hydrogen source for high storage density. • Stable hydrogen generation was obtained for the entire operation time. • Restartability was evaluated to validate the possibility of commercialization. A hydrogen generator using solid-state sodium borohydride (NaBH 4) as a hydrogen source was proposed as part of a high-energy-density fuel-cell system for unmanned aerial vehicles. In this study, solid-state NaBH 4 was used in order to overcome problems of a hydrogen generator using catalytic hydrolysis of NaBH 4 aqueous solution such as low hydrogen yield and unstable hydrogen generation due to catalyst degradation. An agent solution, hydrochloric acid, was injected on to the NaBH 4 to generate hydrogen. In addition, all of the balance-of-plant systems and components were integrated to develop a lightweight, commercially-viable, high-density hydrogen generator. The developed hydrogen generator was evaluated in terms of stable hydrogen generation and restartability for the entire operation time in order to validate the possibility of commercialization. From the performance evaluation, the gravimetric and volumetric specific energy densities of the hydrogen generator were found to be 739.1 W hr/kg and 272.8 W hr/L, respectively. In addition, the hydrogen storage density was 5.1 wt%, which was 1.44 times higher in comparison of a typical hydrogen generator using NaBH 4 aqueous solution. [ABSTRACT FROM AUTHOR]