BRUSSELS, April 15 (Reuters) - EU antitrust enforcers will decide by May 20 whether to clear South Korean chipmaker SK Hynix Inc's $9 billion buy of Intel Corp's NAND memory chip business, according to a European Commission filing.

The U.S. chip giant announced the sale last October, part of a move to divest non-core businesses to focus on its smaller but more lucrative Optane memory business which uses more advanced technology.

The deal is SK Hynix's biggest acquisition, which will help it close the gap with market leader Samsung Electronics Co Ltd . NAND chips are used to store data in smartphones and data centre servers.

SK Hynix sought EU antitrust approval on April 13. The EU competition enforcer can clear the deal with or without concessions, or it can open a four-month long investigation if it has serious concerns.

The U.S. Committee on Foreign Investment last month cleared the deal, while the U.S. Federal Trade Commission gave the green light last year. (Reporting by Foo Yun Chee; Editing by Jan Harvey)