Fitbit shares soared nearly 50% on its initial public offering on 18 June, making it one of the most successful flotations of 2015 so far.
The company, which produces wearable technology that measures various fitness data, offered 36.6 million shares at $20 (£12.6, €17.7) on the first day, raising a total of $732m.
Shares had rose to $29.68 by the day's close on the New York Stock Exchange.
The success of the flotation is especially impressive against the backdrop of Apple's recent launch of the Apple Watch, which contains many health-tracking capabilities.
Fitbit sold 10 million units in 2014, bringing the company's revenue up to $745.4m. This is a 175% rise from 2013.
The San Francisco-based company reported sales of $337m in the first three months of 2015, a 200% year-on-year increase.
Ramon Llamas, wearables research manager at the International Data Corporation, said: "Bucking the post-holiday decline normally associated with the first quarter is a strong sign for the wearables market. It demonstrates growing end-user interest and the vendors' ability to deliver a diversity of devices and experiences. In addition, demand from emerging markets is on the rise and vendors are eager to meet these new opportunities."
Fitbit said it would invest the $732m raised from the flotation into R&D and is considering mergers and acquisitions.