Advanced Micro Devices, the year's best-performing technology stock, got pummeled Monday as the entire tech sector took a nosedive.

Shares of AMD tumbled as much as 11 percent on Monday to a low of $18.80, the biggest decline among the 66 companies in the S&P 500 tech index. AMD closed down 9.5 percent, well below the Information Technology Index, which closed down 3.5 percent.

Despite the setback, AMD is still the top tech gainer of the year, rising more than 85 percent. The stock hit its peak on Sept. 13, when it traded at $34.14, and has since been on a downward spiral, dropping more than 40 percent.