The present disclosure describes epitaxial oxide devices with impact ionization. In some embodiments, a semiconductor device comprises: a first semiconductor layer; a second semiconductor layer coupled to the first semiconductor layer; and a first and a second electrical contact coupled to the second and first semiconductor layers, respectively. The first semiconductor layer can comprise a first epitaxial oxide material with a first bandgap and an impact ionization region. The second semiconductor layer can comprise a second epitaxial oxide material with a second bandgap that is wider than the first bandgap.