Web visibility is the appearance of web sites in search engines. Web visibility in search engine is an important factor to improve the e-commerce on the web. If the web site gets high ranking in search engines it will attract more web traffic. Semantic markup is a technique to structure a web site, so it can be understandable by humans and computers. This allows the crawler or spider to understand the content of the web site during the search engine process. Semantically structured web sites increase the web visibility in search engines. RDFa is a semantic markup and supported by the W3C. In this thesis we have focused on the RDFa as a semantic markup technique. This study shows two aspects of RDFa i.e. what are the benefits and barriers of using RDFa in structuring and enhancing the web visibility of web sites in search engines, and how web developers implement RDFa. This study is based on the data that has been collected through literature review and interviewing different web developers from different companies. First result of this study shows the benefits and barriers of using RDFa according to the web developers. Second result is a guideline for helping the companies that are planning to implement the RDFa in structuring their web sites. The guideline is based on the technical steps and the requirements for implementing RDFa that web developers have described during the interviews.