Shares of Advanced Micro Devices Inc. tumbled 6.2% in afternoon trade Wednesday, putting them in danger of kicking off their second bear market this year. The chip maker's stock was the biggest percentage decliner in both the PHLX Semiconductor Index and the SPDR Technology Select Sector ETF . The stock was trading 21.9% below its Sept. 14, 2018 close of $32.72, which was the highest close since May 2006. Many chart watchers believe a decline of 20% or more from a bull-market peak defines a bear market. The current bear market threshold is a close at or below $26.17. The last bear market for AMD's stock started March 22, 2018, when it closed at $10.91, or 20.6% below the Jan. 31 peak of $13.74. That bear market ended on May 7, when it closed at $11.59, or 21.6% above the bear-market closing trough of $9.53, hit on both April 2 and April 9. Intel Corp. unveiled at a New York event earlier this week its next-generation desktop processor to compete with AMD's Ryzen chips. AMD shares have still run up 54% over the past three months, while Intel shares have dropped 12.8%, the PHLX's SOX has lost 8.0% and the Dow Jones Industrial Average has gained 3.9%.