This paper studies how the maturity distribution of public debt – measured by concentration and skewness – shapes sovereign borrowing costs and the transmission of refinancing risk to financial stability in 20 OECD economies over the period 1995Q1-2020Q4. We construct time-varying Gini and Herfindahl-Hirschman indices over maturity buckets and link them to short- and long-term sovereign yields within a panel framework robust to cross-sectional dependence (Driscoll-Kraay standard errors) and non-stationarity (panel error-correction estimators). Three results stand out. First, debt concentration is a quantitatively important determinant of yields, while the role of maturity skewness is limited outside stress episodes. Second, the concentration yield relationship is significantly stronger in high debt economies, consistent with a state-dependent pricing of rollover risk that interacts with the sovereign-bank nexus […]