Shares in Dialog Semiconductor dropped about 24 percent on Monday after the company acknowledged for the first time that top customer Apple could develop its own battery-saving chips used in iPhones.
The stock has lost half its value since April on investor concerns that Apple is working on its own power chips. Analysts reckon Dialog derives more than half its revenue from supplying Apple with power management integrated circuits (PMICs).
Dialog said there was no risk to its existing supply deals in 2018 and it was in the advanced stages of working with Apple on designing "2019-type products" that could lead to commercial contracts by next March.
"Our position remains that we have seen no material change to our ongoing relationship with Apple," chief executive Jalal Bagherli told investors on a conference call.
However, the Anglo-German chipmaker conceded: "Apple has the resources and capability to internally design a PMIC and could potentially do so in the next few years."
Apple declined to comment.
The Nikkei business daily last week quoted one source as saying Apple would make about half the iPhone's power-management chips starting next year, with another source saying this could be delayed to 2019.
"Even if Dialog is safe for 2019, people are going to question 2020 and if they are safe in 2020, they will question 2021," Credit Suisse analyst Achal Sultania said
"Apple is obviously not helping Dialog to win this argument with investors".
Investors are wary of companies that rely heavily on Apple, which has cut out several small suppliers in the past.
The US technology company said in April it planned to replace graphics chip supplier Imagination Technologies, sending its shares down 70 percent in a single session. Imagination was subsequently sold off in two separate deals.
Semiconductor suppliers are typically barred by Apple from revealing their supply relationships. Dialog, which has previously declined to name Apple, referring to it only obliquely as its "largest customer" or its "main business", said it had received a special dispensation from Apple to mention it.
Dialog stock fell 24 percent to 23.70 euros.
"The shares appear to have instantly priced that Apple will design out Dialog partly or nearly completely," Morgan Stanley said in a note to investors. The brokerage said the reaction could prove overblown and that Apple may still decide to stick with Dialog rather than developing its own power chips.
Bagherli said Apple's feedback so far on 2019 product plans had been "very good" and that he expected to have more clarity by March on the terms of new business from Apple for 2019. Dialog would update investors when it had more details, he said.
The slide in Dialog shares echoed one in April, after Bankhaus Lampe analyst Karsten Iltgen advised investors to sell the stock because Apple was working on its own battery-saving chip.
(Additional reporting by Ludwig Burger in Frankfurt; Editing by Edmund Blair and Mark Potter)