A method of etching a platinum group metal film uses a gas mixture containing argon (Ar), oxygen (O2) and halogen gases and a method of forming a lower electrode of a capacitor uses the etching method. The gas mixture contains O2, Ar, and a third component, preferably a halogen, e.g., chlorine (Cl2) or hydrogen bromide (HBr). In the method of forming a lower electrode, a conductive film containing a metal belonging to a platinum (Pt) group is formed on a semiconductor substrate, a hard mask partially exposing the conductive film is then formed on the conductive film. Then, the exposed conductive film is dry-etched using the hard mask as an etching mask and a three-component gas mixture containing argon (Ar) and oxygen (O2), to form a conductive film pattern beneath the hard mask, and the hard mask is then removed.