A production loss based maintenance plan is proposed to reduce the semiconductor testing cost due to unscheduled ATE (Automatic Test Equipment) downtime. Three maintenance methods, active redundancy, standby redundancy and vendor repair, are proposed and their impacts on the repair time, i.e. the downtime period, are compared under various repair scenarios.By reducing the ATE downtime, the system utilization increases and hence the production loss is mitigated, if not minimized.This method is different from existing approaches such as multiple sites testing or low cost ATE testing. Leveraging the aggregate cost model, decision makers can determine the maintenance method that minimizes the production loss. A numerical example is used to demonstrate the application of the new method. Results show that using redundant modules is a very effective approach to reduce the semiconductor production loss due to unscheduled ATE downtimes.