Etching characteristics of Si1−xGexalloys in ammoniac wet cleaning (RCA cleaning) were examined. The etching rate of Si1−xGexbecame larger with increasing Ge ratio (X). Temperature dependence of the etching rate was studied and the etching rate was large at high temperatures. However, no obvious difference was observed in the temperature dependence of Si1−xGexetching rate at different Ge ratio (X). A surface morhology degradation after RCA cleaning was observed at high Ge ratio (X). A stoichiometry change of Si1−xGexsurface after RCA cleaning was observed by x‐ray photoelectron spectroscopy (XPS). The etching rate increase and the surface morphology degradation are thought to be due to the rapid etching of Ge atoms at the top surface layer.