NEW YORK >> Apple’s market capitalization topped $500 billion in opening trading Wednesday, climbing to a mountain peak where few companies have ventured and none have stayed for long.

Apple was already the world’s most valuable company. The gap between it and No. 2 Exxon Mobil Corp. has widened rapidly in the past month, as investors have digested Apple’s report of blow-out holiday-season sales of iPhone and iPads, and raised their hopes that the company might institute a dividend.

On Tuesday, the Cupertino, Calif., company sent out invites to reporters for an event in San Francisco next Wednesday, apparently to reveal its next iPad model. The launch of the new model was expected around this time, a year after the launch of the iPad 2.

Exxon, now worth $411 billion, was worth just over $500 billion for two short stretches at the end of 2007. Apple’s arch-nemesis Microsoft Corp. was worth just more than $500 billion briefly at the end of 1999, then again in early 2000. It even shot up above $600 billion for one day. The company is now worth $267 billion.

Cisco Systems Inc., Intel Corp. and General Electric Co. also peaked just above $500 billion in early 2000. Cisco and Intel are now worth a bit more than $100 billion each, while GE is worth $200 billion.

Despite its sky-high market capitalization, Apple’s valuation isn’t high compared to its earnings. It’s worth 15 times its earnings for the last year. That compares to 21 times earnings for Google Inc. and 14 times for the S&P 500 overall. Yet few companies in the index grow their earnings as fast as Apple does: In its latest quarter, its earnings rose 118 percent from a year ago, to $13.06 billion.

Apple’s stock accounts for 3.8 percent of the value of the S&P 500 index, according to Standard & Poor’s, and it accounted for 6 percent of the operating income of the 500 companies in the fourth quarter.

Analysts say Apple’s sheer size works against its stock price. Apple stock already makes up a large share of the holdings of technology and growth-focused funds, and they have little appetite for more. Meanwhile, value-focused funds are often prevented from buying the shares because the company doesn’t pay a dividend.

However, the company has been signaling that a dividend is under consideration, and several analysts now consider it a given that one will be announced this year. Last week, CEO Tim Cook told shareholders at the annual meeting that the company has more money than it needs, and the board and management are thinking "very deeply" about ways to use the cash.

Former CEO Steve Jobs, apparently haunted by the company’s lean years in the 90s, had a policy of accumulating cash. The company now sits on $97.6 billion.

In the first few minutes of trading Wednesday, Apple’s market capitalization climbed near $508 billion as shares rose $8.98, or 1.7 percent, to $544.39.