SEOUL, July 27 (Reuters) - SK Hynix Inc said on Friday it planned to invest 3.5 trillion won ($3.1 billion) to build an additional semiconductor plant in South Korea to prepare for growing demand for memory chips.

The new plant to break ground in late 2018 with a target of October 2020 for completion, the world's No. 2 memory chipmaker said in a statement.

The production portfolio for the new plant would be decided later, depending on future market conditions, it added. ($1 = 1,123.6000 won) (Reporting by Heekyong Yang; editing by Richard Pullin)