In a plasma-etching method and apparatus for etching samples of e.g. semiconductor device substrates etc., a sample (24) is cooled and subjected to an etching process with a gas plasma. An acceleration voltage which accelerates ions in the gas plasma towards the sample (24) is repeatedly changed, e.g. by a controller (81). In a process based on low-temperature etching, an etching processing producing no residue, being an anisotropic and being highly selective is realized.