We report new data on the electrooptic behaviour of the semiconductor ferro
electric crystal Sn2P2S6 in the temperature region 295-390 K. At the room t
emperature the magnitude of the effective longitudinal electro-optic coeffi
cient is about 50 pm/V, much larger than the value reported previously. Cor
responding half-wave voltage is less than 500V. We also observed Curie-Weis
s type increase of r(eff) near the ferroelectric phase transition at 339 K.