Non-supersymmetric D-brane configurations with Bose-Fermi degenerate open string spectrum

The spectrum of open strings on various non-BPS D-brane configurations in t ype II string theory on a K3 orbifold is analysed. At a generic point in th e corresponding moduli space the spectrum of open strings does not have any degeneracy between bosonic and fermionic states. However, there exist spec ial values for these moduli for which many non-BPS D-brane configurations h ave an exactly Bose-Fermi degenerate open string spectrum at all mass level s. In this case the closed string exchange interaction between a pair of su ch D-brane configurations vanishes at all distances.