Silicon Valley Bank Collapse: What We Know - The New York Times

Flush with cash from high-flying start-ups, Silicon Valley Bank bought huge amounts of bonds more than a year ago. Like other banks, Silicon Valley Bank kept a small amount of the deposits on hand and invested the rest with the hope of earning a return. 

That had worked well until the Federal Reserve began raising interest rates last year to cool inflation. At the same time, start-up funding started to dry up, putting pressure on many of the bank's clients — who then began to withdraw their money. To pay those requests, Silicon Valley Bank was forced to sell off some of its investments at a time when their value had declined. In its surprise disclosure on Wednesday, the bank said it had lost nearly $2 billion...

https://www.nytimes.com/2023/03/10/business/svb-silicon-valley-bank-explainer.html