Mobile payments startup Square continues to surge ahead. The mobile payments startups today announced closing a fourth-round financing for a reported $200 million at a $3.25 billion valuation. First rumored over the summer, the latest funding comes from Citi Ventures, Rizvi Traverse Management and Starbucks.

The coffee chain announced its $25 million investment in Square in August as part of its wider partnership with the company to power m-payments and credit card transactions in stores. Square also said it’s now processing $8 billion in transactions on an annualized basis, up from $1 billion a year ago. Internally, its headcount has increased from 150 to 400 employees in the last year, with plans to add another 100 to keep up with its rapid growth.

“Square’s growing revenue and workforce preceded the company’s plans for international expansion later this year,” stated its release on Monday. The company’s small card reader allows small businesses to handle card payments using smartphones and tablets instead of traditional point-of-sale (POS) machines. It also charges merchants a fee of 2.75% per swipe or a flat monthly fee of $275.

Square more recently has also introduced its own mobile payment offering for consumers -- Pay with Square -- that allows people to pay for items at participating retailers through its mobile app for iOS and Android devices. Square has raised a total of $341 million to date from investors that also include Sequoia Capital, Visa and Kleiner Perkins Caufield & Byers, according to the Crunchbase database.