TSMC is pouring another $100 billion into its Arizona plants, a bullish sign for the company and for anyone betting on the AI boom.

• The extra money brings TSMC's total US investment to $265 billion, one of the biggest factory buildouts anywhere.
• A company that knows its customers' future orders better than anyone does not spend like that unless demand is still climbing.
• Washington has pushed chipmaking back onto US soil under both Biden and Trump, and TSMC is the biggest beneficiary.
• Spreading factories across the US, Japan and elsewhere also softens the blow if tensions between China and Taiwan ever hit the island's supply chain.
• As the world's largest contract chipmaker, TSMC sits at the center of every AI data center being built.

Outlook: As long as spending on AI keeps rising, TSMC should keep riding the wave — making it a strong buy in the eyes of market watchers.