Amazon emerges as most valuable US firm amid market turmoil

Amazon has eclipsed Microsoft as the most valuable publicly traded company in the U.S. a see-sawing stock market continues to reshuffle corporate America's pecking order

It marks the first time Amazon has held the top spot and ends Microsoft's brief return to the pinnacle after it surpassed Apple in late November .

That's one reason most technology stocks are well off their peaks. Amazon, for instance, remains 21 percent below its high reached in September when the company's stock value stood above $1 trillion. Apple was worth even more back then, but its stock has plunged by 37 percent since early October to erase about $400 billion of its market value.

Apple confirmed some of investors' worst fears last week when it warned that disappointing demand for iPhones, especially in China, caused its revenue for its most recent quarter to fall well below the projections of its management and industry analysts.