The invention relates to a device (1) for continuous heat treatment of granulated materials, especially to the crystallization of polymer granulate, such as polyethylenterephthalate (PET) for example. The device comprises several adjacent fluidization chambers (2, 3, 4, 5, 6) respectively provided with a sieve plate (11) through which a fluidization gas used to fluidize the granulate can be insufflated into the respective chamber from below via a gas inlet (9), said gas being able to escape via a gas outlet (10) in the top area of the device. The first chamber (2) takes up the greater part of the overall volume of all chambers (2, 3, 4, 5, 6) and neighbouring chambers are, respectively, fluidically connected by means of product throughflow openings (18, 19, 20, 21; 28, 29, 30, 31) in the separating walls (14, 15, 16, 17) arranged therebetween. According to the inventive method, using the inventive device (1), the granulated material is guided through several adjacent fluidization chambers (2, 3, 4, 5, 6), the absolute filling level of the fluidized granulating material in the first chamber (2) being at least as high as the absolute filling level of the other adjacent chambers (3, 4, 5, 6) disposed downstream therefrom.