Mitsubishi UFJ Financial Group Inc., Japan's largest bank by market value, may have to raise its $3 billion bid for control of UnionBanCal Corp. after the Californian lender's stock surged.

"The U.S. market is certainly expecting Mitsubishi UFJ to increase the price," David Threadgold, a bank analyst with Fox-Pitt Kelton Asia Ltd. said Wednesday in Tokyo. "It's certainly conceivable that Mitsubishi UFJ will have to raise its bid"

Threadgold said the San Francisco-based bank may be worth close to $70 a share, compared with Mitsubishi UFJ's offer of $63 per share for the 35 percent of the stock it doesn't already own. UnionBanCal's shares rose 13 percent to $65.50 in New York trading overnight.