Its worse, TSMC is the single biggest semiconductor manufacturer for general logic chips. Samsung has their own fabs for ram and ssd's specialised for density. All the litography equipment they use come from a single company called ASML. They also have complete market domination for the past few generations of litography machines and are the first and only producers of EUV litography.

Semiconductors are so complex and capital intensive that even a duopoly couln't balance the expense.