The Ministry of Trade, Industry and Energy said the surplus jumped as August imports rose only 0.8 percent year-on-year to $41.45 billion.
The surplus in July was $2.71 billion and $1.93 billion in August of last year.
"The country posted a trade surplus for the 19th consecutive month in August as its exports further increased, showing signs of a gradual recovery," the ministry said in a release.
The jump in August exports was credited to increased shipments to the United States, up 17.9 percent year-on-year, Yonhap News reported. Shipments to ASEAN countries and China also surged more than 10 percent.
South Korea, Asia's fourth-largest economy after China, Japan and India, is heavily dependent on exports.