Truly bulk In2O3 single crystals were obtained from the melt for the first time using an innovative growth technique, and, for comparative purpose, from the gas phase (PVT). In2O3 undergoes a strong decomposition at elevated temperatures even under high oxygen partial pressure. Bulk single crystals obtained from the melt were dark-brown in color, which changes to greenish upon annealing in a non-reducing atmosphere (i.e. neutral and oxidizing). As-grown In2O3 crystals obtained by the PVT method were dark-green. All melt and PVT-grown crystals had n-type conductivity with electron concentration respectively around 2–3×1018/1.5×1019cm−3, Hall mobility of 145/110cm2V−1s−1 and resistivity of 1.5–2.5×10−2/4–5×10−3Ωcm, where the first value corresponds to melt-grown and the second to PVT crystals. Annealing in the non-reducing atmosphere decreased the electron concentration by one order of magnitude in melt-grown crystals, but produced no effects in PVT-grown In2O3. Annealing of melt-grown In2O3 crystals lead to a metal-semiconductor like transition. Melt- and PVT-grown crystals exhibited cut-off wavelength at 440nm. Melt-grown In2O3 crystals became fully transparent upon annealing. Their visible and IR spectrum showed a sharp absorption edge. The FWHM of the rocking curve of the melt-grown In2O3 single crystals was 28arcsec.