(Bloomberg) -- A Hong Kong court ruled that Tsinghua Unigroup Co. breached a payment support agreement tied to dollar bonds, marking a key victory for creditors in a broader legal dispute over a practice long used by Chinese firms to raise debt.

Most Read from Bloomberg

Unigroup, a semiconductor giant previously affiliated with the elite Tsinghua University, was ordered to pay $483.8 million for failing to honor a so-called keepwell deed meant to backstop its US-currency notes. The lawsuit, filed by bond trustee Citicorp International Ltd. about two years ago, involves a $450 million bond from a Unigroup unit, according to data compiled by Bloomberg.

The note jumped 1.8 cents to 39.5 cents Friday, Bloomberg-compiled prices show, set for the biggest gain in a month.

“The Unigroup ruling is significant in that it illustrates how keepwells can be a source of material credit enhancement,” said Fergus Saurin, the legal adviser to the bondholders behind the trustee’s lawsuit. A keepwell is an agreement from the parent company of a unit issuing a bond to maintain the issuer’s solvency while stopping short of guaranteeing payment.

“While the decision might not herald a keepwell renaissance, if a guarantee is not a commercially or legally practicable option then a keepwell is likely to be one of a range of potential credit-enhancement substitutes under consideration at the structuring stage,” added Saurin, a Hong Kong-based partner at law firm Kirkland & Ellis LLP.

The ruling may revive some confidence in China’s offshore credit market, where the keepwell structure remains a dominant feature for many bonds that have either defaulted or are facing payment risks. Investor mood suffered a setback last month after the same Hong Kong court threw out three of four similar lawsuits against Peking University Founder Group Corp., another major defaulter.