The structural approach views firm's equity as a call option on the value of its assets, which motivates stockholders to increase risk. However, since bank assets are risky debt claims, bank equity resembles a subordinated debt. Using this assumption, and considering the strategic interaction between a bank and its debtor, we argue that risk shifting is limited to states in which the debtor is in financial distress. Furthermore, risk shifting increases with bankruptcy costs and decreases with bank capital. Thus, increasing a bank's capital affects stability, not only through the additional capital buffer, but also by affecting the risk shifting incentive.

Black and Cox (1976) claim that the value of junior debt is increasing in asset risk when the firm's value is low. We show, using closed-form solution, that the junior debt's value is hump-shaped. This has interesting implications for the market-discipline role of banks' subdebt.Final pre-print of a manuscript accepted for publication in Economic Letters.