Mueller Matrix Spectroscopic Ellipsometry (MMSE) has a potential application to CD metrology of vertical nanowire gate-all-around (GAA) transistors. These transistors could be used in memory applications, like 4F2 3D NAND. Simulated sensitivity of MMSE based scatterometry to changes in the geometry of GAA transistors test structures was characterized at a critical etch back process step. MMSE responses to dimension changes were simulated using rigorous coupled wave analysis (RCWA) using commercial Optical CD software. Parameter correlations were evaluated and when possible, approaches for decorrelation are presented to assign specific changes in the Mueller Matrix to a single process change.