Shares of Advanced Micro Devices (NYSE: AMD) are plunging after the unexpected departure of the company chief executive officer, Dirk Meyer.

As of 11:06 a.m. (EDT), shares have dropped 8.16 percent.

Today’s price plunge sharply reverses the strong momentum the stock has enjoyed recently. Shares had soared almost 60 percent from last September through yesterday’s close.

Meyer’s sudden exit has puzzled analysts.

“[The] lack of details behind this resignation as well as its abruptness comes as a surprise to the market and will, in our view, be viewed in a negative light until further details are provided,” wrote Deutsche Bank analyst Ross Seymore in a research note.