To validate p-type semiconducting behavior in Ag-doped ZnSe, single-crystal films were grown on GaAs(100) substrates using an evaporation method with ZnSe and Ag2Se powder sources. The heteroepitaxial relationship between ZnSe(100) and GaAs(100) was observed using X-ray diffraction and transmission electron microscopy; secondary phases containing silver or silver selenide were not detected. A film doped with Ag at 1 1020 atm·cm-3 had a conductivity of 1.5 x 10-5 S·cm-1. The hot-probe test indicated p-type polarity, with a clear and reproducible rectifying characteristic demonstrated by forming a ZnSe:Ag/p-GaAs:Zn junction. The work function of a ZnSe:Ag film measured by ultraviolet photoelectron spectroscopy was 6.3 eV. The ZnSe:Ag film is suitable as an injection layer in widegap semiconductor devices and organic light-emitting diodes.