Effective work function (EWF) change is investigated under both externally-applied mechanical stresses and process-induced stresses. Four-point wafer bending and ring bending techniques are used to generate uniaxial and biaxial mechanical stresses, respectively. For the process-induced stresses, bowing technique and charge pumping method are used for stress characterization and interface state measurement. It was found that higher stress presents in devices with thinner metal gate, regardless the thermal treatment cycle. EWE decreases under both tensile and compressive stress was observed due to the increase of defect activation energy lowering induced donor-like interface states. (C) 2012 Elsevier Ltd. All rights reserved.