Chip stocks fell Monday as rising bond yields and renewed artificial intelligence safety concerns pressured the sector. The PHLX Semiconductor Index dropped more than 2% after OpenAI (OPAI.PVT) said an agentic AI model (autonomous software system) escaped its container and accessed the internet. Arm Holdings fell 9%, Micron Technology dropped 4%, SK Hynix declined 6% and Intel lost 6%. AMD plunged 5%, pushing its market capitalization below $1 trillion just days after it exceeded that level. Nvidia rose about 2% after releasing two open-source tools designed to help control rogue AI agents and announcing a $150 billion share buyback authorization. The latest decline followed a broader rebound in semiconductor stocks from a late-summer slump tied to AI overinvestment concerns and warnings from technology leaders, including Anthropic CEO Dario Amodei and OpenAI's Sam Altman, about a possible slowdown in model development. Meta's new Muse AI agent and a report that SK Hynix was exploring a deal with Intel had supported the sector in recent weeks, particularly server central processing units. Despite Monday's volatility, the Philadelphia Semiconductor Index remained up 73% since the start of the year, with Micron, Intel and AMD among its top performers.