An ultrahigh-frequency (450 MHz) microplasma jet was stably generated at a chamber pressure as low as 10(-3) Pa. Electron and gas temperatures of this microplasma as estimated by optical-emission spectroscopy measurements were similar to 7000 and 1000 K, respectively. The atomic oxygen flux at the torch exit was revealed to be of the order of 10(19) atoms/cm(2) s, which is 10(2)-10(4) times higher than that obtained by other conventional plasma sources. This microplasma jet was also applied as an ion source for in situ neutralization of electron charging-up effects in a scanning-electron microscopy observation of insulating materials.