Apple Inc., the world’s most valuable company, trumped skeptics once again by reporting blowout iPhone sales.

Apple says it sold 35 million iPhones in the January-to-March quarter, almost twice as many as it sold a year ago and above analyst expectations.

Apple’s stock was down 2 percent at the close of regular trading, as investors believed phone companies had reined in iPhone sales. In extended trading, the stock rallied $40.02, or 7.1 percent, to $600.30.

“They’re delivering the goods much stronger than even the biggest bulls would have thought,’’ said Brian White, an analyst with Topeka Capital Markets. “It’s Apple fever at its finest.’’

Net income in the company’s fiscal second quarter was $11.6 billion, or $12.30 per share. That was nearly double the net income of $6 billion, or $6.40 per share, a year ago.

Analysts polled by FactSet were expecting earnings of $10.07 per share for the latest quarter, Apple’s fiscal second.

Revenue was $39.2 billion, up 59 percent from a year ago. Analysts were expecting $37 billion.

IPad sales came in below analyst expectations, at 11.8 million units. But that was still two and a half times as many as it sold in the same quarter a year ago. Apple launched a new iPad model in the quarter, and supplies are still tight. White believes short supplies of the new high-resolution screen are to blame.

Mac sales were also slightly below expectations, at 4 million. That was up 7 percent from last year. Meanwhile, the overall PC market grew about 2 percent.

Windows PC makers are now hoping Windows 8 will give them a better chance at competing with Apple, both in PCs and tablets. Intel CEO Paul Otellini last week said he believes PCs and tablets will merge into one light device with a keyboard and a touch-sensitive screen.