The first experimental demonstration of ferroelectric Al:HfO2 (FE-HAO) FETs is proceeded with negative capacitance (NC) effect. The subthreshold swing (SS) of 40 mV/dec and 39 mV/dec for forward and reverse sweep, respectively, as well as almost hysteresis-free are achieved. The partial orthorhombic phase of FE-HAO is confirmed both with (PMA) and without (PDA) a capping layer. A gradual transition of polarization after 1000°C annealing is obtained with increasing Al concentration for large remanent polarization (Pr), coercive field (Ec), and high dielectric constant. The similar physical thickness (∼7nm) of ferroelectric-HfZrOx (FE-HZO) FET is discussed for comparison. The NC modeling is performed to validate the NC effect for the Al:HfOx material system. The transient behavior is performed at room temperature and low temperature, and the dynamic NC model is discussed.