There's a high demand for chips built using .18 and .15 micron processes, and TSMC is having to outsource some of its work to meet demands.
TSMC is letting Vanguard International Semiconductor (VIS), Ningbo Sinomos Semiconductor Incorporated (NSSI) and Wafer Tech handle some of the orders that it will not be able to deliver on time, the sources said.

Judging from their recent business contacts with TSMC, IC design houses have found that the foundry giant’s order visibility has already been extended to the second quarter of 2006, and that TSMC will be running at full capacity in the first quarter, the sources said.
[Digi Times]