A detailed metallographic characterization of a precipitation hardening semi-austenitic stainless steel is described. A new etching procedure based on the Lichtenegger and Blöch color etching solution, which is frequently used in duplex stainless steels to differentiate delta ferrite from austenite, has been used to differentiate martensite, austenite and the Chi-phase in this stainless steel. By changing the etching conditions, this etchant now reveals the austenite grain boundaries when the steel is in the austenitic state. Moreover, this solution is able to reveal also the prior austenite grain boundaries when the steel is in its martensitic state. This etching procedure represents a great advantage because it reveals, at the same time, different features of the microstructure.