The structural and thermal properties of ferroelectric semiconductor TlGaSe2 with layered crystalline structure have been investigated in 77-300 K temperature range. It is found that all outlined physical properties of TlGaSe2 are significantly modified near 180 K due to the phase transition (PT). The nature of this PT has been analyzed and it is established that the main peculiarity of such PT is the extreme sensitivity to interlayer bonding. As a result, any manifestations of this PT depend strongly on defects and impurities located between the layers and can be changed by illumination, temperature annealing and applying electric field. (C) 2011 Elsevier Masson SAS. All rights reserved.