Affected by Apple's overly-optimistic expectations for sales of the iPhone X, inventory of finished chassis, and other parts and components at the iPhone X's supply chain makers are still hovering at persistent high leveles at the end of June 2018, almost equaling to three times of what they had shipped previously, according to sources from Taiwan's handset supply chain.

Since some chassis and other components for older-generation iPhone devices can also be used for the production of next-generation iPhone products, these component suppliers are eyeing the planned launch of the new iPhones this fall to bring a sales boom that will effectively clear out their inventory, said the sources.

Nevertheless, Apple's performance has not been affected by the inventory pile-ups at component suppliers, the sources noted.

Based on Apple's financial report for the second quarter of 2018, the company shipped a total of 52.217 million iPhone devices in the quarter, up 3% from a year earlier, while iPhone revenues were up 14% on year to US$38.032billion during the same period thanks to the high ASP of iPhone X products.

The supply chain makers pointed out that they have been willing to cope with Apple's demand to build up inventory due to the company's proven records for cooperation previously, but they were caught by surprise this time.

But some suppliers, instead of lodging complaints against Apple, attributed the inventory issue to the dwindling global smartphone market, which is expected to grow a mild 4.9% in 2018 compared to a 10% growth recorded in 2015.