A beam plasma was generated and exhausted into air by applying rf voltage to the atmospheric pressure argon flowing through a cylindrical gap between a needle cathode and a grounded cylindrical anode whose surface was covered with an insulator. This torch‐type plasma with gas and electron temperatures of 240 °C (44.2 meV) and 1.0 eV, respectively, has been verified to be useful for ashing a photoresist without using a pumping system. High rate (≥1.2 μm/min) photoresist ashing was achieved by using Ar plasma containing a small amount of oxygen. Also reported are optical emission analysis of plasma and analyses of ashed Si surface by scanning electron microscopy. Fourier transform infrared spectroscopy, electron microprobe analysis, and x‐ray photoelectron spectroscopy. The use of the Pt cathode was found to provide not only a better ashed surface but also a higher ashing rate than the use of the stainless‐steel cathode.