CBS will make a cash tender offer for all issued and outstanding shares of CNET for $11.50 a share. The deal will give CBS a combined 54m unique users a month, and approximately 200m users worldwide.
Leslie Moonves, president and CEO of CBS, said: "There are very few opportunities to acquire a profitable, growing, well-managed internet company like CNET Networks. CBS stands for premium content and unparalleled reach, and CNET Networks will add a tremendous platform to extend our complementary entertainment, news, sports, music and information content to a whole new global audience.
"Together, CBS and CNET Networks will have significant additional exposure to the fastest-growing advertising sector and can accelerate our growth through a number of new content, promotion and advertising initiatives. We could not be more pleased with the prospect of adding CNET Networks and its tremendous team of people to the CBS family."
Based in San Francisco, CNET Networks owns a slew of online entertainment, news and information sites, which also include mp3.com, CNET news.com, UrbanBaby, CHOW, Search.com, BNET, MySimon and TechRepublic.
The company, which reported significant profits in 2007 on revenues of $406m has a large international footprint, particularly in China.
CBS will combine CNET Networks' sites with its own, which include CBS.com, CBSSports.com, CBSNews.com and UK social website last.fm, which CBS bought in May 2007 for £141m.
Neil Ashe, CEO CNET Networks, said: "CNET Networks operates some of the most important premium online brands, serving the most sought after online audiences. Today's announcement brings together two organisations that complement each other and working with Leslie, Quincy and the talented people at CBS, we look forward to taking our business and our brands to the next level."
The board of directors of CNET has unanimously approved the merger agreement and unanimously recommends that CNET Networks stockholders accept the tender offer and tender their shares.