This paper proposes a semantic extension to the Materials Science Markup Language, “MatML”, which serves as XML for Materials Property Data, thus forming a standard for information exchange. Since MatML is developed for Materials Science in general, its structure is not sufficient to store specific information related to the Heat Treating of Materials. This motivates the development of an extension for capturing the semantics of Heat Treating, in particular, its rapid cooling step, namely Quenching. At CHTE-WPI, a “Quenching Element” is being proposed as an extension to MatML to include Heat Treating semantics. The new element is proposed as a MatML extension, rather than as an independent markup language, because several aspects in Quenching have to be stored in conjunction with basic Materials Science information. For example, the properties of a material such as “thermal conductivity” would need generic storage using MatML, while the details of its heat treatment such as “fluid agitation” would be stored in Quenching. The “Quenching Element” thus aims to be a part of a MatML document structure, at the same level as its existing “Material Element”. The proposed extension is designed with the goal of providing a uniform standard to store and exchange Quenching documents in a semi-structured format. This provides a seamless store for numeric, textual and graphical data. Issues such as synonyms, homographs and other domain specific aspects are addressed through the development of a good ontology. Since the design is done using XML schema, it is possible to query the documents using XQuery, a Query Language for XML. Thus the searching of Quenching data is also facilitated, in addition to its storage and exchange. Just as MatML heads towards being a widespread standard in Materials Science, the proposed semantic extension aims to do so in Heat Treating, with particular emphasis on Quenching.