Qualcomm (QCOM - Get Report) shares traded sharply lower Thursday after the world's biggest smartphone chipmaker forecast weaker-than-expected December quarter revenues following Apple Inc's (AAPL - Get Report) decision to use Intel (INTC - Get Report) chips in its new iPhones.

Qualcomm posted a loss of 35 cents a share for the three months ending in September, its fiscal fourth quarter,  and said a one-time tax boost would help end-December earnings rise to as high as $1.15 per share on sales of between $4.5 billion and $5.3 billion. Both figures, however, missed analysts' forecasts, and the company Apple's move towards Intel chips would hit both its top and bottom line and Qualcomm didn't update its existing full-year earnings guidance.

"The combined impact of Apple instructing their contract manufacturers to stop paying their contracted royalty payments and Apple's decision to use a competitor's modem for their latest device has had a significant impact to our financial performance," CEO Steven Mollenkopf told investors on a conference call late Wednesday. "Notably, over 50% of the expected fiscal 2019 headwind related to Apple is reflected in our first fiscal quarter guidance and impacts our QCT business. As we progress through the year, this will become less impactful to our quarterly results."

Qualcomm shares were marked 7.15% lower in trading Thursday, a move that would extend the stock's year-to-date decline past 8% and value the San Diego, Calif.-based tech group at just under $90 billion.

Apple opted to dump Qualcomm chips from its new iPhone suite amid a long-running legal dispute over patents and imports, one of which is currently being argued before the U.S. International Trade Commission.

Qualcomm is also suffering from a wane in global smartphone demand, which is affecting first quarter shipments of its Snapdragon MSM chips. Qualcomm sees MSM units deliveries of around 185 million units, a figure that missed most analysts' forecasts.

"In fiscal 2019, we expect relatively flat global handset average selling prices and low to mid-single-digit percentage handset sales growth year over year, with strength coming from the emerging regions, providing solid end market trends for (Qualcomm's licensing business) once the licensing disputes are resolved," CFO George Davis told investors late Wednesday.