The crystal structure, temperature-dependent electrical conductivity, Hall coefficient, current-voltage characteristics, absorption spectra and temperature- and illumination-dependent photoconductivity of Tl3InSe4 single crystals were investigated. Tl3InSe4 crystallises in a body-centred lattice with tetragonal symmetry and belongs to the space group [image omitted]. The crystals are extrinsic p-type semiconductors and exhibit a conductivity conversion from p- to n-type at a critical temperature, Tc, of 283 K. They are observed to have Schottky diode properties in an Ag/Tl3InSe4/Ag Schottky barrier device structure. The absorption spectra displays two maxima, one related to an indirect energy band gap of 1.20 eV and another corresponding to exciton transitions. The photocurrent is observed to be strongly affected by the conductivity type of the crystal. The incident light intensity dependence of the photocurrent is found to be supralinear, linear and sublinear, indicating strong recombination at the surface, monomolecular recombination and bimolecular recombination, respectively, in the regions where the sample is p-type ([image omitted]), at [image omitted], and in the n-type region ([image omitted]). In the n-type region, the photocurrent increases with decreasing temperature down to 250 K, below which the photocurrent is temperature invariant. The change in recombination mechanism is attributed to the change in the behaviour of sensitising and recombination centres.