South Korean shares reversed early gains and finished lower on Monday, following declines in U.S. stock futures despite strong trade data.

The won weakened despite official pledges to stabilize markets, and the benchmark bond yield edged higher.

The Korea Composite Stock Price Index or Kospi fell 6.22 points, or 0.2%, to end at 3,920.37. The Kosdaq increased by 9.71 points, or 1.1%, to close at 922.38.

In economic news, South Korea booked a trade surplus of $9.7 billion in November, marking the highest figure since September 2017 and above October's trade surplus of $6 billion.

Exports increased by 8.4% to $61 billion in November from a year earlier, which was stronger than the median increase of 5.7% as expected by economists in a Reuters poll and the previous month's addition of 3.5%.

Imports in the month also added 1.2% on-year to $51.3 billion, the Korea Customs Service said in a Monday release.

Inbound shipments failed short of economists' expectations of a 3.4% rise, as well as marked a decline from an increase of 1.5% in October.

Meanwhile, semiconductor shipments surged 38.5% year on year to a record monthly high of $17.26 billion.

In corporate news, Fadu (KOSDAQ:440110) secured an order from unnamed NAND flash memory manufacturers for the supply of enterprise solid-state drive (SSD) controllers, according to a Monday filing with the Korean Exchange.

Shares of the company fell nearly 2% at market close.