SNAP III, a 3- to 5-watt electrical generator, was designed as a proof- of-principle device in the development of radioisotope-powered thermoelectric power-conversion systems. A program involving five development areas was employed in achieving this aim. These areas were: (1) generator development, fuel encapsulation, and handling techniques; (2) system safety studies; (3) system dynamic tests; (4) system parametric performance tests; and (5) system life tests. Particular attention was given to fuel encapsulation and handling techniques, system safety studies, system parametric performance tests, and system life tests. (auth)