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What: Shares of Volterra Semiconductor (NASDAQ:VLTR) plunged today by as much as 11% after the company reported earnings.

So what: Sales in the fourth quarter added up to $40.3 million, resulting in net income of $4.6 million, or $0.18 per share. On a non-GAAP basis, net income came out to $7.1 million, or $0.28 per share. Both sales and adjusted earnings topped consensus estimates.

Now what: Full-year sales totaled $168 million and adjusted earnings per share were $1.24. CEO Jeff Staszak said 2012 was the company's 12th consecutive year of revenue growth and ninth consecutive profitable year. The company also acquired Element Energy, a small start-up that specializes in battery technology, for an unspecified amount. Investors are possibly skeptical about the acquisition.

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