Wafer starts measures the number of raw wafers entering the fabrication process per unit time (typically per month). It's the primary metric for fab production volume and capacity planning.

Typical Fab Wafer Starts Per Month (WSPM)

• Small/specialty fab: 5,000-15,000 WSPM • Mid-size fab: 20,000-40,000 WSPM • Large high-volume fab: 50,000-100,000 WSPM • TSMC mega-fab (e.g., Fab 18): 100,000+ WSPM

Wafer Starts vs. Wafer Outs

Wafer starts = wafers entering the fab. Wafer outs = wafers completing all process steps and shipping. The difference is the WIP (work-in-progress) in the fab. During ramp-up, starts exceed outs as the fab fills with WIP. At steady state, starts ≈ outs (with a lag of ~2-3 months cycle time).

Why Wafer Starts Matter

Revenue forecasting: More wafer starts → more wafer outs → more die production → more revenue (with yield factored in). Capacity planning: Wafer starts relative to installed capacity determines utilization rate. Customer commitments: Foundries commit capacity to customers as wafer starts per quarter. Supply chain signal: Industry-wide wafer start data indicates overall semiconductor demand health.

Wafer Start Decisions

Fabs don't blindly maximize starts. Customer orders drive starts at foundries. Demand forecasts drive starts at IDMs. During downturns, companies deliberately reduce starts to avoid building excess inventory. During shortages, fabs run at maximum starts and customers compete for allocation.