 Shares of Magnachip Semiconductor Corp. shot up 15.8 in premarket trading Friday, after the South Korea-based chipmaker confirmed that it received an unsolicited buyout bid representing a premium of more than 50. The company said Cornucopia Investment Partners, on behalf of itself and a group of investors, has offered to buy all of Magnachips outstanding shares for 35 in cash, which is 51.8 above Thursdays closing price of 23.05 and would value the company at about 1.66 billion. 