To provide a Ga2O3 compound semiconductor device in which a Ga2O3 system compound is used as a semiconductor, which has an electrode having ohmic characteristics adapted to the Ga2O3 system compound, and which can make a heat treatment for obtaining the ohmic characteristics unnecessary.An n-side electrode 20 including at least a Ti layer is formed on a lower surface of an n-type β-Ga2O3 substrate 2 by utilizing a PLD method. This n-side electrode 20 has ohmic characteristics at 25° C. The n-side electrode 20 may have two layer including a Ti layer and an Au layer, three layers including a Ti layer, an Al layer and an Au layer, or four layers including a Ti layer, an Al layer, a Ni layer and an Au layer.