Apple shares close above $400

Apple (s aapl) shares hit a milestone on Tuesday, closing at $403.61. It’s the first time the company’s stock has ever closed above $400.

The stock price of the iPhone and iPad maker hit $400 a few times Monday, but closed at $398.50. Today shares opened at $400 and peaked earlier this morning at $404.48.

There’s no mystery where the boost is coming from. Apple’s stock value has been swinging steadily upward since the introduction of the original iPad in late January 2010. Since then, Apple shares have grown 96 percent. Most recently, Apple reported blow-out third-quarter 2011 earnings last week, on the back of sales of more than 20 million iPhones and 9 million iPads in just three months.

Apple’s market capitalization is the number that Wall Street has been eyeing perhaps even more closely. As of Tuesday, Apple is worth $374.18 billion, making it the second-most valuable company in the world after ExxonMobil(s xom). While Apple is close, Exxon still has a pretty sizable lead, closing today with a valuation of $415.52.

But there’s at least one good reason to believe Apple’s value for shareholders isn’t going to lose steam anytime soon: Still expected sometime later this year is the next iteration of the iPhone.