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Visitors walk past a Samsung Galaxy tablet advertisement during the Mobile World Congress in Barcelona Feb. 28, 2012. Reuters

Massive competition from the electronics industry has dramatically shrunk the lead the iPad gave Apple Inc. (NASDAQ:AAPL), the most valuable technology company, over the past two years, market researcher IDC said. While still the leader in fourth-quarter shipments, Apple lost its majority share.

Nevertheless, the Cupertino, Calif., electronics developer still controlled 43.6 percent of the tablet market, IDC said, with a record 22.9 million shipments of iPads and iPad Minis. But that share fell from 51.7 percent a year earlier.

Making huge inroads was archrival Samsung Electronics Corp. (KRX:005930), with 15.1 percent of the market, selling 7.9 million units. A year earlier, the Korean giant’s share was only 7.3 percent.

The share of Inc. (NASDAQ:AMZN), the No. 1 e-retailer, fell as well, to an estimated 11.5 percent from 15.9 percent a year earlier, when it launched the new Kindle Fire line. IDC estimated the Seattle-based company sold only 6 million units, compared with 4.7 million a year earlier.

Amazon didn’t release tablet sales figures when it reported fourth-quarter results this week. It has never disclosed them. But IDC, of Framingham, Mass., and its rivals often receive this kind of confidential data.

Taiwan’s Asustek Computer (TPE:2357) ranked fourth, with 5.8 percent share on 3.1 million shipped tablets, a solid improvement over its year-earlier 2 percent share on 600,000 units.

Barnes & Noble (NYSE:BKS), the No. 1 bookseller, was ranked fifth, with only a 1.9 percent share on a million units, down from the prior-year’s 4.6 percent share on shipments of 1.4 million e-readers. During the year, the New York-based company took in $300 million from Microsoft Corp. (NASDAQ:MSFT), the No. 1 software company, to develop a new device.

Other vendors had 22.1 percent of the market, shipping 11.6 million tablets, a solid gain above the 18.4 percent share with 5.5 million tablets in the fourth quarter of 2011.

New entrants including the Nexus from Google Inc. (NASDAQ:GOOG), the No. 1 search engine, and Surface from Microsoft Corp. (NASDAQ:MSFT), the No. 1 software company, were lumped among “others.”

“We expected a very strong fourth quarter, and the market didn’t disappoint,” Tom Mainelli, IDC research director for tablets, said.

Shares of Apple fell $2.81 to $452.68 in late Friday trading, continuing their 2013 slide. They’ve lost 15 percent so far this year. Samsung shares fell slightly in Seoul.