Very few, if any I imagine. Taiwanese, while Chinese, are still distinct in their language, culture, upbringing etc... Taiwan is a small place, and they can spot a mainlander, a twinge in an accent, and outsider from a mile away. It sounds like the culture in TSMC is also quite strict, uniform and hierarchical, like that of a military unit, making it even harder for a mainland spy get in, or succeed within it.
They aren't infected with American "political correctness" or stupid genuflecting to "diversity." I highly doubt they are hiring any mainlanders for assignment in Taiwan or USA. If anyone were to spy for chicoms, it would more likely be an individual Taiwanese who would be a traitor
Just a guess from my experiences with both
In short, you can’t Shanghai a ChiCom into Peking on semiconductors, or there’ll be hell Taipei.