South Korea's economy posted trade surplus for 78 months to July due mainly to strong demand for locally-made semiconductors and oil products, customs office data showed Thursday.

Revised figure for trade surplus was 6.9 billion U.S. dollars in July, staying in the black since February 2012, according to the Korea Customs Service.

Export, which accounts for about half of the export-driven economy, gained 6.2 percent over the year to 51.8 billion dollars, while import advanced 16.4 percent to 44.9 billion dollars.

The export growth was driven by demand for semiconductor and oil product, of which exports jumped 31.1 percent and 45.4 percent, respectively.

Auto parts shipment rose 6.6 percent, but those for automobiles and ships posted a double-digit reduction.

Exports to China and the United States, South Korea's top two trading partners, grew 27.3 percent and 8.8 percent each, with those to the European Union (EU) and Vietnam expanding 7.1 percent and 7.7 percent, respectively.

Crude oil import surged 63.2 percent last month amid higher global oil price, sending raw material import jumping 31.8 percent.

Import of consumer and capital goods increased 8.1 percent and 1.0 percent each in July.