A U.S. jury found Samsung had copied critical features of the hugely popular iPhone and iPad and awarded Apple $1.05 billion in damages in the most closely watched patent trial in years.
Shares in Samsung - the world's biggest technology firm by revenue - tumbled as much as 7.5 percent, its biggest daily percentage drop in nearly four years, to 1.183 million won, versus a 0.5 percent drop in the broader market.
Trading volume was heavy, more than doubling the last week's daily average by early Monday trade.
"An adjustment in the next few days is unavoidable as the damage amount was much bigger than market expectations, and there are further uncertainties such as the possibility of a sales ban," said John Park, an analyst at Daishin Securities.
Analysts estimate Samsung's earnings will be reduced by 4 percent this year due to increased patent-related provisioning.
The jury at a federal court in San Jose, California, found on Friday that Samsung infringed on six of seven Apple patents. The verdict, which came after less than three days of jury deliberations, could lead to an outright ban on sales of key Samsung products and will likely solidify Apple's dominance of the exploding mobile computing market.
EYES ON GALAXY S III
Apple plans to file for a sales injunction against Samsung, its lawyers said, and the judge in the case set a hearing date for September 20.
Top executives at Samsung, led by vice chairman Choi Gee-sung and head of its mobile division JK Shin, held an emergency meeting on Sunday.
The biggest concern for Samsung remains whether its latest flagship product the Galaxy S III, which was not included in the case, will be also targeted by Apple and included in the list of products banned in the U.S. market. The model is Samsung's best selling smartphone, with sales topping 10 million since its late May debut.
But Samsung's skill as a "fast executioner" - quick to match others' innovations - would likely mean tweaked, non-patent infringing devices would be on the market soon after any ban came into place, analysts said.
"The ruling is a costly lesson for Samsung - but also an opportunity for a true alternative to Apple's well-known hardware with more innovative thinking and imaginative products ahead," Morgan Stanley analysts said in a note.
"There are more ways to build a touch screen smartphone and thanks to its fast execution capability, Samsung could quickly work around design changes, upgrading models and introducing new technology such as flexible displays, Galaxy S III and Galaxy Note to differentiate its devices from Apple."
Samsung was disappointed by the verdict and plans to keep the legal fight to have its claims accepted, according to internal memo sent to its employees, that was seen by Reuters.
"We've sought to settle this through negotiations, as Apple is our customer but had no choice but to counter sue," the memo said. "There's no firm in history which has sustained growth by trying to stifle competition with legal fights on patents, rather than fairly compete with innovation in the market place."