Ever-shrinking yields around the world have left the U.S.looking like a gold mine to Japanese banks.

Mizuho Financial Group Inc., for example, is rapidly expandingits American credit business. The Tokyo-based bank has nearlydoubled its company-debt originations team since April, accordingto Jerry Rizzieri, Mizuho Securities USA Inc.'s head of fixedincome. It's also added a collateralized loan obligation (CLO)group within the past year.

The allure is easy to understand: There's billions of dollars tobe earned off companies racing to lock in cheap borrowing costsbefore the Federal Reserve raises interest rates. And there'smore money in the trading frenzy that sales usually prompt—whichoffer a more attractive proposition in the U.S. than in Japan,where government bonds have negative yields.

“The U.S. market has been a focus of the organization now for anumber of years,” Rizzieri said. “There's still significant upsidefor us.”

The Japanese bank bought more than $36 billion of North Americanloans from Royal Bank of Scotland Group Plc earlier this year,hiring about 40 people from RBS as part of the transaction,according to Rizzieri.

Of course, not everything is so great in the U.S. bankingindustry. If you just listened to the gloom and doom out of somebanks, you'd probably want to run.

Canadian Imperial Bank of Commerce is withdrawing from its U.S.credit business, people with direct knowledge of the situation saidlast month.

JPMorgan Chase & Co. will cut thousands of jobs over thenext year, said a person with knowledge of the plans last week. AndBank of America Corp., the second-biggest lender, sees reducingexpenses in its markets division unless revenue improves, ChiefExecutive Officer Brian Moynihan said on May 27.

Japanese banks, meanwhile, see greener pastures in the U.S.,where top-rated dollar-denominated bonds yield 2.9 percentagepoints more than similar debt in Japan. That's the most since thebeginning of the year, according to Bank of America Merrill Lynchindex data.

Underwriting Rankings

As U.S. corporate bond sales have boomed, Japanese banks havegrabbed a bigger piece of the pie. Companies have sold $670.5billion of U.S. investment-grade bonds in 2015—the most ever forthe period—generating an estimated $3.3 billion of fees for thefirms that managed the offerings, data compiled by Bloombergshow.

Mizuho, Mitsubishi UFJ Financial Group Inc., and Sumitomo MitsuiFinancial Group Inc. have all steadily climbed the ranks ofcorporate-debt underwriters during the past few years.

Mizuho has risen three spots to become the 12th most-activeunderwriter for U.S. investment-grade bond sales this year, up fromNo. 17 in 2012, according to Bloomberg data that strips outself-led offerings.

Mitsubishi has climbed one spot since 2014 to become the 13thmost-active manager, Bloomberg data show. Sumitomo Mitsui ranks20th this year, up from 23rd in 2014 and No. 35 the yearbefore.

These Japanese banks see plenty of room to make moneyunderwriting and trading debt in the world's biggest economy, evenas others seem to be pulling away.