SoftBank Group Corp.’s 2.65 trillion yen ($23.5 billion) initial public offering for its telecom unit was fully subscribed, including an extra allotment of shares, people familiar with the matter said.

The underwriters were able to cover their entire book by Wednesday, thanks to strong demand from retail investors in Japan and overseas buyers, said the people, who asked not to be identified because the information isn’t public. Brokers are collecting more orders from individual investors, which will probably push the stock above the preliminary price of 1,500 yen apiece when trading begins on Dec. 19, they said.

Including an overallotment of about 160 million shares, SoftBank is selling a total of roughly 1.76 billion shares in the telecoms business. Representatives of SoftBank and the lead underwriters declined to comment on the book-building process.

The shares of SoftBank fell 4.9 percent in Tokyo on Thursday, after reversing a steeper decline following the news that the IPO was fully subscribed. A mobile service outage in the afternoon didn’t appear have a significant impact.

SoftBank is set to announce the final offering price on Monday. The figure is unlikely to change, even amid a global stock sell-off that’s dragged the Nikkei 225 Stock Average down for three straight sessions this week. That’s because additional demand for the stock may also come from institutional investors, who will be purchasing…