Mitsubishi is trying to expand beyond its relatively stagnant home market as Japanese companies seek to broaden their presence abroad and take advantage of a weaker dollar.
Mitsubishi raised its bid to slightly more than $73 a share, these people said, up from the $63 a share offer it made last week.
Its first unsolicited offer, made in April, was for $58 a share.
UnionBanCal had rejected Mitsubishi’s bids as “not in the best interest of UnionBanCal’s minority stockholders.” Some analysts had predicted last week that Mitsubishi would raise its offer to at least $70 a share, adding that UnionBanCal has not spurned its Japanese majority stakeholder outright.
Shares in UnionBanCal have risen 42 percent over the last month, buoyed by Mitsubishi’s offer. They closed at $65.49 a share on Friday.
Mitsubishi has said that its proposed acquisition of UnionBanCal, one of California’s largest banks, would be a “first step” in a new strategy, one many analysts think involves buying other American institutions.