What's happening: Shares of Ambarella (NASDAQ:AMBA) were down 15% as of 10:45 a.m. Monday, continuing last week's sell-off after short-seller Citron Research referred to the HD video processing chip company's valuation as "ridiculous," assigning a $60 price target on its shares. The stock closed Thursday at $126.70.

Why it's happening: Citron didn't stop there with the colorful language on Friday, saying that Ambarella's "parabolic frenzy has now launched it into a realm that can't possibly be supported by reality." Citron further fears Ambarella's products will ultimately face risk of commoditization, leaving the stock trading at much lower multiples, similar to other chip-making peers.

To be fair, even after today's drop Ambarella stock has more than doubled so far in 2015, and trades at a seemingly lofty 52 times trailing-12-month earnings. But it also looks much more reasonable at around 28 times next year's estimates. And Ambarella has shown a propensity for trouncing expectations in recent quarters, with growth supported by much more than just its key relationship with GoPro.

In the end, while it's hard to blame investors for taking some of their quick gains off the table, I also wouldn't be the least bit surprised if Ambarella resumes its upward climb from here.