Samsung closed at 1,480,000 won on profit-taking led by foreign investors, with analysts saying the release of the Galaxy S4 had already been factored in and investors were concerned the share price had hit a ceiling.
"It's not because the Galaxy S4 failed to meet expectations. It's just that investors feel technical smartphone upgrades are flattening out," Bae Seung-Young of Hyundai Securities told AFP.
The broader market was down 0.78 percent.
Kang Hyun-Chul of Woori Securities said foreign investors had dumped Samsung to lock on gains, adding IT companies tended to adjust downward following the release of new products.
The Galaxy S4, which will roll out in 155 countries in late April, has a high-definition, five-inch (12.7-centimeter) screen, enhanced picture-taking capabilities and the capacity to translate to and from nine languages.
Samsung's share price has held steady this year, while rival Apple has tumbled 20 percent as disappointing sales of iPhones raised fears that its dominance may be slipping.
The South Korean giant captured 29 percent of the smartphone market in 2012, to Apple's 21.8 percent, and 23 percent of the overall mobile phone market, ahead of Nokia's 17.9 percent.