The dielectric constant of metastable ϵ-Ga2O3 was evaluated for the first time by using a transparent heteroepitaxial structure of ϵ-Ga2O3/indium tin oxide/yttria-stabilized zirconia. The dielectric ϵ-Ga2O3 layer was grown by the facile solution route of mist chemical vapor deposition at atmospheric pressure. The highest dielectric constant of nearly 32 (at an AC frequency of 10 kHz) was about three times larger than that of the most stable β-Ga2O3 phase. This high dielectric constant is attributed to the polar structure of ϵ-Ga2O3 unlike β-Ga2O3, and is comparable to those of the so-called high-κ dielectric oxides. The combination of a wide bandgap and a high dielectric constant would be beneficial for the future development of optoelectrical devices.