When depositing amorphous SrTiO3 (STO) films on crystalline STO substrates by pulsed laser deposition, metallic interfaces are observed, though both materials are band-gap insulators. The interfacial conductivity exhibits strong dependence on oxygen pressure during film growth, which is closely related to the STO plasma expansion in the background gas of oxygen. By controlling the charge balance in the STO plasma with an external bias, Vbias, of −10 V ≤ Vbias ≤ 5 V at an oxygen pressure of 10−4 Pa, the interfacial conduction can be tuned to be metallic or semiconducting. These results provide a new opportunity to tailor low-dimensional interface states of complex oxide heterostructures.