A cohomological property of semi-abelian $p$-groups

We prove a cohomological property for a class of finite $p$-groups introduced earlier by M. Y. Xu, which we call semi-abelian $p$-groups. This result implies that a semi-abelian $p$-group has non-inner automorphisms of order $p$, which settles a longstanding problem for this class. We answer also, independetly, an old question of M. Y. Xu about the power structure of semi-abelian $p$-groups.