A Ga2O3-based semiconductor element includes an undoped β-Ga2O3 single crystal film disposed on a surface of a β-Ga2O3 substrate, a source electrode and a drain electrode disposed on a same side of the undoped β-Ga2O3 single crystal film, a gate electrode disposed on the undoped β-Ga2O3 single crystal film between the source electrode and the drain electrode, and a region formed in the undoped β-Ga2O3 single crystal film under the source electrode and the drain electrode and including a controlled dopant concentration.