Apple plans to hold a 'Mac Event' next Wednesday that will include a preview of the next version of the Mac operating system, CNBC has learned.

Apple shares topped $300 for the first time on Wednesday as stellar iPad sales and a planned expansion into China continued to give investors high hopes for the iPhone maker's already healthy prospects.

Shares of Apple (NASDAQ: aapl) climbed nearly $2.50 in morning trading after rising to a record $301.72 earlier in the session. This gives Apple a market capitalization of about $275 billion, above tech heavyweights such as Microsoft (NASDAQ: msft), Google (NASDAQ: goog) and Hewlett-Packard (NYSE: hpq).

Apple has been on a tear lately, with sales of the iPad tablet surpassing expectations. Investors also have high hopes for Apple's push into China, where the iPhone maker is looking to open 25 retail stores next year.

Mounting speculation about a Verizon (NYSE: vz) iPhone as soon as 2011 is also adding to Apple's appeal. Currently, the iPhone is only available from AT&T (NYSE: att). in the U.S.

Morgan Keegan analyst Tavis McCourt said the recent $400 million acquisition of app developer ngmoco by Japan's DeNA is also a huge plus for Apple. Ngmoco is known for the games it makes for the iPhone, though it also plans to release apps for Android devices soon. Even so, McCourt said the pricey acquisition means even more app developers will flock to Apple's devices, where they have the best chance to make the most money.