Shares of Shake Shack Inc. (NYSE:SHAK) soared 8 percent Thursday as the fast-casual burger joint explores adding chicken sandwiches to its menu, according to a recent filing. The stock hit a new 52-week high of $90.52 Thursday, after closing at a record high of $82.85 a day earlier. Shares have gained more than 20 percent this week following the company's strong earnings last week. 

Shake Shack’s subsidiary SSE IP recently applied for a trademark filing for "chicken shack." The company has yet to reveal its plans, but the filing shows the “chicken shack” name is for chicken sandwiches.

Shake Shack’s chicken dog, a hot dog made with chicken, apple and sage sausage, is the only menu item currently with chicken.

The company’s flagship burger restaurant in Madison Square Park reopened this week, more than seven months after it closed for renovations. Restaurateur Danny Meyer opened the company's first location in Madison Square Park in 2004.

Shares of Shake Shack soared 132 percent during their first day of trading on Jan. 30, to close at $48.77. The company and its bankers had priced the initial public offering at $21 per share. Since then, the stock has surged 95 percent, valuing the company at nearly $3 billion.

Last week, the New York-based company said its revenue jumped 56 percent from a year earlier last quarter, its second quarterly earnings report since going public. Same-Shack sales, a key metric used to measure its business at locations that have been open for at least two years, leaped 11.7 percent in the first quarter, compared with 3.9 percent during the same period in 2014.

“From an operational standpoint Shake Shack has not only been impressive with Same-Shack sales, but they’ve also done a great job staying on track with their expansion plans,” Research firm Estimize said in a note last week. “So far Danny Meyer’s team is proving that they can keep their promises.”

The company plans to use the proceeds from its IPO to open new stores and renovate existing ones. The company opened 10 U.S. stores in 2014 and plans to open at least 10 new domestic stores each year beginning in 2015, for the foreseeable future.

Shake Shack opened two new locations in Boston and one in Baltimore this quarter, and plans to expand its footprint to at least 450 stores by opening eateries in new and existing markets both in the U.S. and abroad.

There are currently more than 60 Shake Shacks worldwide in nine countries, including Dubai, Istanbul, London and Kuwait.