1. Would it thus cost the same to operate such a fab in the US?
2. Why did the US outsourced the semiconductor fabrication in the first place? Was it more labour intensive in the past?
Taiwan does not have dramatically lower taxes than US, but there is something particular to how working capital is accounted which will make for a double digit difference in the in TW vs. US.
Third is supplies. Even before the semi moving to Asia, US fabs had to import a big portion of their supplies.
2. > Why did the US outsourced the semiconductor fabrication in the first place
Why did US outsource almost everything, even when it makes no sense?
It simply tough, tedious, problematic doing business in the US.
I wrote about it many times before here.
You mind your own business, very much literally. Few month down the line some trouble comes: lawsuit, taxmen, utilities, creditors, SEC, city hall, suppliers, random activists, labour union... pick any.
Building a fab requires labor, a lot of it.
Imagine, where they get their workers? They import them all from their home countries.
Similar consolidations have happened in the past and in other industrial fields. This time, two of the three surviving champions are simply not American.
There are more people sitting in offices there than on the floor.
I fact there is a huge oversupply of semiconductor engineers globally because of fabs becoming less, and less labour intensive.
Companies take a big effort to reduce the number of people on the floor futher, but now not so much for labour cost readon, but security. The chance of somebody who shouldn't really be on the floor acidentally pressing the wrong button, and sending $10M worth of wafers down the drain is the risk they don't want to take.