Samsung took 20 percent of the market, up from 8.8 percent a year earlier, according to Framingham, Massachusetts-based IDC. Apple’s share dropped to 15 percent from 17 percent, while Nokia Oyj’s fell by more than half to 14 percent. Apple had taken the top spot worldwide in the second quarter, IDC said.

Samsung, based in Suwon, Korea, is riding a wave of popularity for devices built on Google Inc.’s Android software, including the Samsung Galaxy S II. Android phones, also made by HTC Corp. and Motorola Mobility Holdings Inc., have greater variety than Apple’s iPhone and tend to be cheaper than the latest Apple models.

“Samsung’s ascendancy to the leadership position is the direct result of its broad and deep product portfolio,” Ramon Llamas, senior research analyst at IDC, said in a statement.

HTC, based in Taoyuan, Taiwan, cracked the top five for the first time, boosting its share of shipments to 11 percent from 7.1 percent a year earlier, IDC said. Research In Motion Ltd., maker of the BlackBerry smartphone, fell to 10 percent from 15 percent.

A 50 percent drop in U.S. sales last quarter pushed RIM’s U.S. market share down to 9 percent in the third quarter from 24 percent, the research firm Canalys said earlier this week. HTC and Samsung both sold more smartphones in the U.S. than Apple did in the third quarter, Canalys said.

IDC’s Llamas said Samsung may have a difficult time maintaining its top position, especially with Nokia introducing new phones that run on Microsoft Corp.’s Windows Phone software.

“Samsung’s position will be a challenge to maintain,” added Llamas. “Apple’s fourth-quarter launch of the iPhone 4S and lower pricing of older models will certainly boost volumes, and Nokia’s recent launch of Windows Phone smartphones marks the beginning of a new era for the company.