The present disclosure describes methods and epitaxial oxide devices with impact ionization. A method can comprise: applying a bias across a semiconductor structure using a first electrical contact and a second electrical contact; injecting a hot electron, from the first electrical contact, through a second semiconductor layer, and into a conduction band of a first epitaxial oxide material; and forming an excess electron-hole pair in an impact ionization region of the first semiconductor layer via impact ionization. The semiconductor structure can comprise: the first electrical contact; the first semiconductor layer with the first epitaxial oxide material with a first bandgap coupled to the first electrical contact; a second semiconductor layer with a second epitaxial oxide material with a second bandgap coupled to the first semiconductor layer; and a second electrical contact coupled to the second semiconductor layer, wherein the second bandgap is wider than the first bandgap.