Raising capital on wholesale debt markets is an important source of funding for banks and non-banking institutions throughout the world. We investigate the determinants of wholesale funding costs for the Global Systematically Important Banks (G-SIBs) using credit default swaps, the proxy for the cost of wholesale debt funding. Using 25 G-SIBs which are heavily reliant on debt capital markets across multiple currencies, this paper investigates whether the default risk of the interbank lending system, i.e., LIBOR-OIS spread is a new global macroeconomic factor in determining G-SIBs’ CDS spreads. Based on time-fixed effects and bank-fixed effects, we find default risk from the US banking system seems to play a greater role in explaining the wholesale funding costs of the G-SIBs than that of their home-country equivalent default risk. Overall, the findings make an important contribution to domestic and international debt funding markets and provide an insight for financial intermediaries, regulators, and monetary-policy makers.