Using GGA+U approach based on the density functional theory, the on-site correlation and the electronic structure of wurtzite zinc oxide are investigated. By atomic population analysis, the zinc 3d orbital is found to be almost fully filled, but the oxygen 2p orbital is partially filled. So, the zinc oxide can be approximately regarded as a sort of d10 semiconductor. Similar to that of d0 magnets found previously, the on-site Coulomb repulsion of 2p orbital in such a d10 system is shown to be also indispensable in addition to that of 3d orbital. As the unconventional on-site Coulomb repulsion of O 2p is considered, the theoretical results agree with the previous experimental observations satisfactorily. The partial density of states shows significant OZn hybridization in the valence band, but it decreases a little as the on-site correlations are taken into account. © 2013 Wiley Periodicals, Inc.