Shares in the tech giant hit a high of $664.75 (£422.50) in Monday morning trading, valuing the company at more than $619bn. The price topped the $618.9bn Microsoft achieved in December 1999.
In January, Apple surpassed oil firm Exxon Mobil for the first time to become the most valuable company on the planet. It now dwarfs Exxon's $405.6bn market value by more than $213bn.
The company's shares dropped dramatically in July as sales figures disappointed analysts, even as profits rose 21% year-on-year to $8.8bn (£5.6bn).
But shares have risen again on rumours that Apple is planning to launch a smaller version of its top-selling iPad and is close to making a new push in the TV market, which has long been a target for chief executive Tim Cook.
The company's share price was $378.55 on 5 October 2011, the day that Steve Jobs, co-founder and the driving force behind the firm's most famous products, died. Since his death, Apple has gone on to report record sales, and its share price has soared.
Apple's landmark high comes as Facebook's shares hit new lows on Monday, sinking to less than half their initial public offering price and halving the fortune of founder Mark Zuckerberg.
By mid-morning, Facebook's shares hit a new low of $18.75 (although recovered to close at $20.01), less than half the $38 they were sold for in May amid the most heavily hyped stock sale in recent history. The slump has knocked close to $10bn off the value of Zuckerberg's stake in the firm, which is now worth about $9.5bn.
Facebook's recent share slide comes after the expiration of a lock-up period that allows some of its earliest investors to sell more of their shares. The expiration increased the pool of available shares by 60% and confirmed analysts' fears that it might lead to more falls in Facebook's already battered share price.
Some of Silicon Valley's most prominent investors are among those now able to reduce their holdings. Details of which large shareholders have decided to cash in are not yet available.
Facebook's share price faces a series of other potential challenges in the next few months as more lock-up periods expire and staff are allowed to sell shares.
Facebook's fall comes as its peers, too, have faced investor scepticism. Shares in Groupon, the daily deals site, are also close to new lows and early investors including Marc Andreessen, one of Silicon Valley's most respected investors, have been cutting their holdings.
Shares in Zynga, the online games company, have fallen over 68% since last year's initial public offering. The firm, whose hits include Words With Friends and Draw Something, was responsible for 12% of Facebook's revenue last year.
On the day of its IPO in May Facebook was briefly valued at more than $100bn, more than the combined worth of Nike and Goldman Sachs. The social network is now valued at $40.61bn.
The company is on course to claim a billion people as users this year. But while its size and reach are undisputed, analysts fear that the firm has been unable to find a way to make money from its mobile users, the fastest growing sector of its business.
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