NEW YORK — Shares in the mobile payment services company Square rose sharply Friday after Visa disclosed the details of its ownership stake in the company.

While Visa’s stake amounts to about 1 percent of the company, and the stake was established at least 5 years ago, investors interpreted the announcement as a major endorsement of Square by Visa, the world’s largest payment processing company.

The disclosure is how major investors disclose an existing stake in a company. Because Square only went public three months ago, this is the first time the public is getting details about Visa’s ownership.

If Visa were to convert its 4.2 million Class B shares into Class A shares, it would make Visa the second-largest owner in Square behind Capital Research & Management’s 12.7 percent stake.

Square shares rose 8 percent Friday to close at $9.30.