Let F be a number field unramified at an odd prime p and F∞ be the Zp-cyclotomic extension of F . Generalizing Kobayashi plus/minus Selmer groups for elliptic curves, Büyükboduk and Lei have defined modified Selmer groups, called signed Selmer groups, for certain non-ordinary Gal(F /F )-representations. In particular, their construction applies to abelian varieties defined over F with good supersingular reduction at primes of F dividing p. Assuming that these Selmer groups are cotorsion Zp[[Gal(F∞/F )]]modules, we show that they have no proper sub-Zp[[Gal(F∞/F )]]-module of finite index. We deduce from this a number of arithmetic applications. On studying the Euler-Poincaré characteristic of these Selmer groups, we obtain an explicit formula on the size of the Bloch-Kato Selmer group attached to these representations. Furthermore, for two such representations that are isomorphic modulo p, we compare the Iwasawa-invariants of their signed Selmer groups.