Samsung Electronics shares fell the most in more than seven weeks in Seoul trading after the company rested its case in a patent-infringement trial with Apple in California.

The stock of the world's largest maker of TVs and mobile phones dropped as much as 4 per cent, headed for the biggest decline since June 25, and was the biggest drag on the MSCI Emerging Markets Index.

Samsung, a key supplier and competitor of Apple, had rallied 23 per cent from July 12 through yesterday as it forecast higher demand for panels and handsets, and retained its position as the world's biggest phone seller.

Samsung rested its case in the trial after putting on witnesses who said Apple would owe the South Korea-based company as much as $421.8 million in royalties.

Apple sued Samsung in April 2011, accusing it of copying patented designs for mobile devices such as iPhones, and the South Korean company countersued.

"There seems to be some profit-taking interest, especially as the recent gain has brought the stock close to its previous high," Song Myung Sup, an analyst at HI Investment and Securities, said by phone today.

"Uncertainty over upcoming rulings on legal battles with Apple is also weighing on sentiment."

Apple accounts for about 9 per cent of Samsung's revenue, making it the company's biggest customer, according to a Bloomberg supply-chain analysis.

Samsung is the exclusive manufacturer of Apple-designed chips for iPhones and iPads.

Samsung, the world's biggest maker of dynamic random-access memory chips, also dropped on speculation that this month's declines in prices for the computer-memory devices may be more than expected, Lim Dori, an analyst at Shinyoung Securities, said.

Samsung traded at 1,296,000 won, down by 3.6 per cent, as of 1.28 pm in Seoul.

Bloomberg