Google Inc. (Nasdaq: GOOG)’s Android operating system powered half of all smartphones bought in the U.S. in the past six months, according to a survey by Nielsen Inc., a sign the software’s market share continues to grow.

Android’s share of new smartphone purchases was double that for Apple Inc. (Nasdaq: AAPL)’s iPhone, at 25 percent, the research firm said in a report today, based on a survey in March about devices bought during the previous half year. Research In Motion Ltd. (RIMM)’s BlackBerry had 15 percent, Nielsen said.

Android’s share of the smartphone market has grown as more handset makers including Motorola Mobility Holdings Inc. and Samsung Electronics Co. use the free Google software. Rising sales will help it to account for half of the total smartphone market in 2012 as Motorola, Samsung and others push into emerging markets with customers looking for cheaper alternatives to the iPhone, Gartner Inc. said this month.

The Nielsen survey in March found that 31 percent of consumers looking to buy a new smartphone planned to buy an Android device, up from 26 percent in a 2010 survey. Apple accounted for 30 percent of planned purchases, down from 33 percent in 2010. RIM’s share dropped to 11 percent on intended purchases from 13 percent last year.

Google, based in Mountain View, California, climbed $11.24, or 2.1 percent, to $536.29 at 12:48 p.m. New York time in Nasdaq Stock Market trading. Apple dropped $1.39to $351.62 and RIM rose 85 cents to $54.29.

Developer Interest

The proliferation of applications, or apps, on Android and Apple devices has helped drive the growth of those two platforms. The number of phonemakers choosing Android, however, has led to a fragmentation of the operating system which makes it harder for developer to build a single app for Android, according to a new study.

“Interest in Android has recently plateaued as concerns around fragmentation and disappointing results from early tablet sales have caused developers to pull back from their previous steadily increasing enthusiasm for Google’s mobile operating system,” according to the study by Appcelerator Inc. and Framingham, Massachusetts-based research firm IDC.

The number of developers “very interested” in building for Android dropped to 85 percent in April from 87 percent in January, in the survey of more than 2,700 developers. The number for Apple dropped to 91 percent from about 93 percent, the survey showed.

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