Square’s IPO Just Got A Bit Bigger by Dan Primack @FortuneMagazine November 24, 2015, 5:10 PM EST E-mail Tweet Facebook Linkedin Share icons Payment technology company Square Inc. SQ today announced that its IPO underwriters exercised their option to purchase an additional 4.05 million shares at the IPO price of $9 per share. That increases the size of Square’s IPO from $243 million to $279 million, and means that the offering is officially closed. Square originally priced its IPO last Wednesday night below its proposed $11-$13 range, and began trading the following morning on the New York Stock Exchange. It initially popped more than 40%, before settling in over the past few days at between $11 and $12 per share. The San Francisco-based company’s current market cap is nearly $3.9 billion, while its fully-diluted value is north of $5.5 billion. Goldman Sachs GS , Morgan Stanley MS and J.P. Morgan JPM served as lead underwriters for the IPO, and were joined by six other groups. During such offerings, the underwriters often are given the option of purchasing a certain number of shares at the IPO price – as happened in this case – via a mechanism known on Wall Street as a “greenshoe.” Square is led by founder and CEO Jack Dorsey, who also co-founded and runs Twitter TWTR .