NEW YORK, Jan 11 (Reuters) - U.S. private equity firm Stonepeak Infrastructure Partners, which specializes in infrastructure investment, has raised $3.5 billion for its second fund.

Stonepeak, which manages $5.7 billion, said the fund-raising was completed in six months and the firm had met its fund-raising target.

New York-based Stonepeak is founded by two former executives of Blackstone, the world's largest alternative asset manager, and invests in infrastructure such as water treatment plants and solar power generators.

Infrastructure funds are appealing to some institutional investors due to their stable long-term returns that are higher than ultra-low government bond yields.

(Reporting by Koh Gui Qing; Editing by Cynthia Osterman)