The stock was up nearly 6 percent at $51.52 after the decision, after earlier spiking to a new 52-week high of $53 a share.
The U.S. International Trade Commission will make recommendations to President Donald Trump, who will decide whether to take actions to protect U.S. manufacturers. Potential remedies could include tariffs on imported solar panels and modules.
The White House said the solar industry contributes to the country's "security" and "prosperity," but noted it would "examine the facts" before imposing tariffs, Dow Jones reported.
First Solar not only designs and manufactures solar panels but also creates systems to help them run. The Tempe, Arizona-based firm also provides operation and maintenance to power plants.
Falling solar panel prices have made it harder for manufacturers like First Solar to turn a profit. Last year, First Solar announced it would take $500 million to $700 million in impairments as part of a plan to expedite development of a new model of solar panel.