Radio frequency (RF) thermal plasma treatment is studied for the size reduction and the spheroidization of coarse glass particles to change them into submicrometer-sized powders of spherical shape. Such ultra-fine spherical powders are the key ingredients of a sintering aid to achieve efficient package and high performance in ceramic electronic applications. The coarse glass powders injected into the high-temperature RF thermal plasma undergo rapid heating, melting, and evaporation, followed by quenching, and then condense to very fine spherical powders. In the thermal plasma treatment with high RF powers of 18-23 kW at a powder feeding rate of 3 g/min, the scanning electron microscopy images and the particle size distribution graphs obtained from the treated glass powders indicate that most glass powders with initial average diameters of around 2 mu m are reformed into spherical ones with sizes of below 500 nm. It is also observed in a 4 MHz RF thermal plasma reactor that the maximum size of particles decreases down to 200 nm when the reactor is operated under conditions of reduced pressure, low powder feeding rate, and high RF power. The compositions of glass powders before and after the plasma treatment are compared by using the wet and the inductively coupled plasma-optical emission spectroscopy analyses. Negligible composition changes appear within a range of < 2 wt% during the RF thermal plasma process, which demonstrates the successful preparation of submicrometer-sized glass powders in spherical shape applicable to the advanced ceramic electronic devices.