Berkshire Hathaway, the investment company of US billionaire Warren Buffett, has sold almost half of its stake in US personal computer maker HP. Buffett's firm made the announcement in a report to regulators on Monday. Berkshire owned 51.5 million shares of HP at the end of November, leaving it holding a 5.2 percent stake in the company. At the beginning of October, Buffett's firm owned about 97.85 million HP shares.