I get much bigger numbers.
10 big fabs is less than 15% of Chinese demand.
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In December 2020, global monthly capacity of semiconductors was 21 million wafers per month (200mm equivalent)
So if you wanted to add an additional 50% of current global capacity inside China, you could need the following combination:
38x Huge Fabs (120,000 wafers per month @ 300mm)
AND
131x Large Fabs (80,000 wafers per month @ 200mm)
Once domestic Chinese technology is mature, China could start mass-producing semiconductor equipment.
I imagine it would be like producing dumplings / sausages.
Due to economies of scale and lower costs, theoretically Chinese semiconductors would be the LOWEST cost in the world.
And yes, a big problem would be finding customers for this capacity.
But also ramping up expertise in operating the fabs and designing chips.
But remember that memory chips are commodities and have the biggest demand. Plus they are most cost effective at older process nodes which use DUV lithography.