Samsung Electronics lost about $12 billion in market value and suffered its steepest one-day slump in more than nine months on Friday on jitters about sales of the South Korean electronics giant’s Galaxy S4 smartphone.

The selloff comes as Samsung and Apple (AAPL) remain in a heated battle in the smartphone world.

Selling was sparked in part by a cautious note from J.P. Morgan Chase (JPM), which warned shipments of the flagship Galaxy S4 for the third quarter will likely “disappoint” investors and cause worse-than-expected margins at Samsung, Dow Jones Newswires reported.

J.P. Morgan analyst J.J. Park said his supply-chain checks reveal monthly orders have been slashed 20% to 30% to as low as 7 million units, Dow Jones reported.

The steep slide also comes just a day after Bloomberg News reported Apple plans to launch an iPhone trade-in program this month in an effort to encourage consumers to upgrade to the iPhone 5. Given the tight competition between the two companies, it’s possible a successful trade-in program could eat into GS4 sales.  

Shares of Samsung closed down 6.2% to the lowest level in four months, representing their worst day since losing a key legal battle against Apple in late August.

For its part, Cupertino, Calif.-based Apple slid 0.89% to $435.00 Friday morning, leaving it down 18% on the year.

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