What's the "next TSMC" (as an investor?)

TSMC is just beginning to reap the rewards of its market dominance. Samsung is a similarly promising investment, but they are listed in South Korea, which is normally inaccessible to Western investors. If you're convinced of TSMC I'd also look into shorting Intel. That bird has flown.

XSD is a good ETF for semis

I would look at the smaller Chinese (not SMIC) ones. Without looking I'd guess they are already highly valued. I have no idea though how long it could take to overtake TSMC/Intel/Samsung.