The business world kicked off the new week with a flurry of mergers and acquisitions on Monday, including one of the largest buyouts in history as U.S. hospital operator HCA Inc. (HCA) agreed to be acquired for about $21 billion.

Under the terms of the deal, HCA, founded by the relatives of Sen. Bill Frist, will be bought by a group of investors for $51 per share, a premium of about 6.5 percent over the hospital chain's closing stock price of $47.87 on Friday.

Other deals announced on Monday included Advanced Micro Devices (AMD), Intel's arch-rival, which confirmed reports it's agreed to buy Canada's ATI Technologies Inc. for $5.4 billion.

• Click here for more on the AMD-ATI deal.

Also, three sets of venture capital groups - including one led by KKR - are in talks to buy Philips Electronics' semiconductor unit for more than $10 billion, The Wall Street Journal reported.

And KKR on Monday was in exclusive talks to buy France Telecom's 54 percent stake in directories unit PagesJaunes for about 3.3 billion euros.

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The HCA buyout group included Bain Capital; Kohlberg, Kravis Roberts, and Merrill Lynch (MER), and HCA management.

The group will assume about $11.7 billion in debt in addition to the $21 billion.

Dr. Thomas Frist Jr., the senator's brother and a board member of HCA, founded the company with his father in the 1960s. He is joining with the private equity groups to acquire the operator.

Last year, federal prosecutors and the Securities and Exchange Commission launched an investigation of Sen. Frist's sale of HCA stock from his blind trusts. The sale occurred in June 2005 near the 52-week peak of HCA share's price and shortly before the stock fell 9 percent.

Sen. Frist, who is considering a 2008 run for president, said he sold the stock to avoid the appearance of a conflict of interest.

The acquisition would rank among the largest leveraged buyouts in history, behind KKR's $25.07 billion agreement to buy tobacco and food industry giant RJR Nabisco in 1988, according to research firm Dealogic. KKR also assumed $6 billion in debt.

The deal marks the latest push by private equity firms, flush with funds of more than $10 billion each, to pursue larger targets.

The boom in private equity deals in the last 18 months is being fueled by low interest rates, liberal debt markets, and record amounts of investor money moving away from lackluster equities into buyout funds.

Merrill , Bank of America Corp. (BAC), Citigroup's (C) Citigroup Global Markets, and J.P. Morgan (JPM) are advising the private equity consortium on the deal.

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Reuters and the Associated Press contributed to this report.