SEOUL, May 21 (Reuters) - South Korea's exports for the first 20 days of May rose 1.5% from the same period a year earlier, customs agency data showed on Tuesday.

Exports of semiconductors rose 45.5%. By destination, exports to the United States and China gained 6.3% and 1.3%, respectively.

On average per working day, exports were up 17.7%. (Reporting by Jihoon Lee; Editing by Tom Hogue)