- Dialog Semiconductor fell in European trading after Bankhaus Lampe downgraded the firm to sell from hold.
- Investors are growing concerned over Apple customer concentration risk. CNBC screened for which firms have 20 percent or more sales exposure to the iPhone maker.
It's not been a great month for some Apple suppliers: Shares of two companies plunged on concerns over their sales contracts with the iPhone maker.
Europe-based Dialog Semiconductor fell more than 15 percent on Tuesday morning after Bankhaus Lampe cited "strong evidence" Apple was developing its own power management chips. Noting that more than 70 percent of Dialog's revenue comes from Apple, the firm lowered its rating on the company's shares to sell from hold.
"We have been observing much stronger interest in engineers of analogue and power management chips from Apple in its hiring activities for a little over a year. We believe that Apple is setting up power management design centres in Munich and California," analyst Karsten Iltgen wrote in the note to clients Tuesday. "We believe Dialog is facing significant uncertainty. Customer diversification seems more important than ever."
Dialog's downgrade comes a week after Imagination Technologies sank more than 60 percent on April 3. The fall was due to the announcement that Apple will not use the company's graphics technology in the future. Apple is also the largest customer for Imagination.
As a result of these two big share declines, CNBC searched for which companies rely on Apple for more than 20 percent of their sales.
Here are the companies with large Apple exposure risk, according to FactSet.
— CNBC's Anita Balakrishnan contributed to this story.