Although there is no unified definition of financial systemic risk (Borio, 2011; Bisias et al., 2012), an operational systemic risk measure can be constructed as a hypothetical insurance premium against catastrophic losses in a banking system (Huang et al., 2009). To construct this premium, we followed the structural approach of Vasicek (1991) for pricing portfolio credit risk, which is also consistent with the Merton (1974) model of an individual firm’s default risk. The two key default risk factors, the probability of default (PD) of individual banks and the asset return correlations among banks, are estimated from credit default swap (CDS) spreads and stock return co-movements, respectively.