Paul Sakuma / AP Media and entertainment company CBS Corp. is buying CNET Networks Inc. based in San Francisco.

SAN JOSE — CBS announced plans Thursday to buy CNet for $1.8 billion, a match that would combine an old-school television network with one of the Internet's pioneers.

The deal would instantly give CBS a top-10 presence on the Internet. At the same time, it likely will help CNet appease shareholders who have pressed for changes amid frustrations about the company's stock performance and business execution.

"There are very few opportunities to acquire a company like CNet Networks," said CBS Chief Executive Officer Leslie Moonves in a statement. "CNet will add a tremendous platform to extend our complementary entertainment, news, sports, music and information content to a whole new global audience."

"We're thrilled to join CBS and combine our interactive media experience with CBS' world-class content," CNet CEO Neil Ashe added in the statement.

Under the deal, which CNet's board has approved, CBS will pay $11.50 a share for the San Francisco-based online media company. That represents a 45 percent premium to CNet's closing price on Wednesday of $7.95 a share.

CNet expects to maintain a large degree of independence under CBS, Ashe said in an interview. Although it will be combined with CBS' Interactive division, CNet will maintain its San Francisco headquarters. Its Web properties — CNet, BNET, Gamespot, Chow and the like — will remain distinct sites and brands, said Ashe, who plans to remain with CNet after the merger.

The combination should help both companies, he said. Both will have opportunities to cross-promote their sites to visitors and advertisers.

Some CNet sites are natural fits for what CBS is doing. CNet owns Radio.com and TV.com, for instance, sites that have appeal to a company that is one of the Big Three TV networks and owns one of the largest radio networks.

"I think we'll help them, and they'll help us," Ashe said. "This is a great opportunity to grow our company going forward."

It's too early to say whether CNet will have any layoffs under the merger, but Ashe said the deal was "not about cost savings."

The deal is in the form of a tender offer in which CBS will buy shares directly from shareholders. The companies expect CBS to formally make the offer to shareholders next week, Ashe said. The companies expect the deal to close in the third quarter.

Growth in online advertising has been outpacing the growth in more traditional media, prompting established media companies to find ways to tap into that growth.

"They're using CNet properties as a way to broaden their appeal," said Sarah Rotman Epps, an analyst who covers the online media industry for Forrester Research. She said the purchase should increase CBS' value to online advertisers.

CBS' move follows a string of similar acquisitions by traditional media companies. In 2005, the New York Times acquired search site About.com and Dow Jones bought MarketWatch. In a similar attempt to boost its online efforts, Microsoft recently attempted to buy Yahoo, but later called it off after refusing to meet Yahoo's price demand.

MarketWatch had been part of an earlier push by CBS to establish itself online. The site had been partly owned and operated by CBS prior to its sale to Dow Jones. CBS also tried to market CBS SportsLine to compete with ESPN.com and Sports Illustrated's SI.com.

— Distributed by McClatchy-Tribune Information Services.