This paper highlights some of the challenges faced for the modeling of MOSFET devices for operation at cryogenic temperature (CT). A special focus is given on the modeling of the threshold voltage V-T and the subthreshold swing SS. The significant increase of V-T at CT reduces the available overdrive voltage and therefore needs to be modeled properly. The SS saturates to a constant value below a critical temperature T-c of typically 40K. This mitigates the current saving that could be expected from reducing the temperature since the transconductance for a given current does not scale inversely with 1/T below T-c. A correct modeling of these two phenomena is therefore key for developing an improved compact model (CM) that scales with T from RT down to CT.