De-embedding structures (transmission lines, open, short) are costly, whether in terms of silicon area or measurement time. In addition, they lead to measurement inaccuracies increasing with frequency in the millimeter-wave bands. In this paper, we show the possibility to perform de-embedding of HEMT transistors measurements through EM simulations in order to extract the unity-gain cut-off frequency (fT). Only an open must be measured to calibrate the EM simulation. Several de-embedding techniques are studied and compared up to 67 GHz, based on measurements or EM simulations. The agreement for the extraction of fT between measured or EM-simulated de-embedding structures validates the proposed approach.