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 Amazon.com 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.