Apple made news throughout the tech world Tuesday when it announced its new product line of MacBooks and iPads in San Francisco. 

One investor hoping to capitalize on Apple' success, is activist investor Carl Icahn, who said he has increased his stake in Apple, while urging the company to make an immediate offer of buyback of shares to boost its stock price. 

The announcement was made in an open letter to Apple CEO Tim Cook on Shareholder's Square Table, a shareholder activism site Icahn launched. Icahn said Apple is currently sitting on $147 billion of cash pile, which is forecasted to generate $51 billion of earnings before income tax next year.

According to the letter, Icahn now owns 4.7 million Apple shares, which are worth $2.5 billion and represents 0.5 percent of the company. Icahn's reasoning for the share buyback comes from the belief that "the market continues to dramatically undervalue the company." Suggesting that Apple buy back shares, Icahn hopes the idea would give an immediate boost to Apple's stock, currently priced at $525. 

"The criticism we have as shareholders has nothing to do with your management leadership or operational strategy," Icahn wrote. "Our criticism relates to one thing only: the size and timeframe of Apple's buyback program. It is obvious to us that it should be much bigger and immediate." 

The latest sales figures of Apple products, including its iPads and iPhones, will be revealed next Monday when the last quarter's results are released. Currently, shares of Apple are down 25 percent from their September 2012 peak of just over $705. 

Building a $20 billion fortune from a series of hostile takeovers, Icahn has a long history of taking positions in companies that give him enough power to force changes in management or provide dividends to shareholders. Icahn also has stakes in Netflix and Twitter.