A method of increasing the intrinsic viscosity of polyester by means of solid state polymerization, wherein a polyester plastics melt is granulated and after granulation is conveyed into a thermal treatment container (13) for thermal treatment therein, the granules being produced slightly below their melting temperature and being fed into the thermal treatment container (13) immediately after granulation so as to utilize the residual heat in the granules, as well as an arrangement for increasing the intrinsic viscosity of polyester by means of solid state polymerization with a granulating and a thermal treatment unit, with an unheated, thermally insulated container (13) or a container (13) having wall heating means (15) being provided as the thermal treatment unit, which is directly connected to the granulating unit via a conveying device (11, 36, 37).