Abstract 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.