Here's a little excerpt from a Motley Fool article on SPIL:
What's even better is having one company that can act as a proxy for that big market. That's what we have in semiconductor packaging and testing specialist Siliconware Precision Industries (Nasdaq: SPIL). One look at Siliconware's results will tell you how the whole chip industry is doing.
Though about 75% of Siliconware's revenue comes from fabless customers like Broadcom (Nasdaq: BRCM) and NVIDIA (Nasdaq: NVDA), large designers with some in-house manufacturing lines like Intel (Nasdaq: INTC) and SanDisk (Nasdaq: SNDK) also use Siliconware's chip testing and packaging services. So when the company's order book dries up, it's a sure sign of deep and dark malaise in the entire sector.
Like SPIL, SNDK reported blowout earnings and gave a great forecast going forward. Yet another SPIL customer doing very well.