Imports increased 26.0 percent from a year earlier to $71.1 billion, leaving a record trade surplus of $49.9 billion, according to the Korea Customs Service.
The record came despite fewer working days, with September having 21.5 working days compared with 24.0 a year earlier.
Average daily exports more than doubled by 104.9 percent to a record $5.63 billion, exceeding $5 billion for the first time.
Semiconductor exports also set a monthly record, the customs agency said.
The Ministry of Trade, Industry and Resources (MOTIR) said chip shipments soared 263 percent from a year earlier, while exports excluding semiconductors also rose 23 percent.
September's result marked another sharp increase from $98.3 billion in August and surpassed the previous monthly export record of $102.0 billion set in June.
Semiconductor exports had already reached a record $46.7 billion in August, up 209 percent from a year earlier, before setting another high in September.
The September figures pushed exports in the first nine months of the year to $814.5 billion, up 56.8 percent from a year earlier and above $800 billion for the first time.
The nine-month tally also exceeded Korea's full-year 2025 exports of $709.3 billion, which had been the country's annual record.
Imports totaled $562.1 billion in the January-September period, up 19.7 percent from a year earlier, leaving a cumulative trade surplus of $252.5 billion.
Korea had already surpassed its 2025 full-year export record on Sept. 5, 117 days before the end of the year, prompting MOTIR to say annual exports of $1 trillion were coming into view.
Reaching that threshold would put Korea alongside the United States, China and Germany as countries that have recorded annual exports of at least $1 trillion, according to MOTIR.
AJP Takeaways
- South Korea's September exports hit a record $120.9 billion, topping $120 billion for the first time.
- Semiconductor exports surged 263 percent to a record, while exports excluding chips also rose 23 percent.
- The trade surplus reached a record $49.9 billion, while nine-month exports surpassed $800 billion for the first time.
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