Other Apple suppliers, like Broadcom and Skyworks Solutions, also traded in the red. Apple is down 3 percent this week.
Apple debuted a new MacBook laptop earlier in the week, and announced Wednesday it would delay its next earnings announcement by a day, now slated for April 26. Apple earnings are expected to be closely tracked by Wall Street for signs the smartphone market is reaching saturation.
"Overall, we view the iPhone as a product line that is maturing," McCourt wrote in a research note. "We still expect a rebound in iPhone trends with the iPhone 7 this fall, but are generally more sanguine than street consensus."
— Reuters and CNBC's Gina Francolla contributed to this report.