We have investigated the effects of substrate surface irradiation with nitrogen plasma prior to growth on the initial stages of the heteroepitaxy of ZnSe on Si(111). The reflection high-energy electron diffraction (RHEED) patterns during the pulsed molecular beam epitaxial growth of ZnSe on the N-plasma-treated Si surface showed very well-defined streaks with a twofold reconstruction indicating an atomically flat surface. In sharp contrast, during the initial stages of the ZnSe growth on untreated Si substrates, spotty RHEED patterns with a diffuse background were observed. A strong evidence of the two-dimensional ZnSe nucleation obtained on the N-plasma-treated Si surface was the clear presence of large-amplitude RHEED oscillations. Atomic force microscopy measurements confirmed that we have achieved a substantial improvement on the ZnSe heteroepitaxy on Si substrates. We show that this novel N-plasma substrate treatment is useful for the growth of other Zn-chalcogenides compounds on Si substrates.