In order to improve frequency characteristics, AlGaN/GaN HEMTs were designed by reducing sourcedrain spacing, optimizing gatestructure and peripheral structure. The devices have been fabricated with domestic GaN epitaxial wafer and process. Measurements indicated that the AlGaN/GaN HEMTs can operate at Kaband. At VDS=30V, the HEMTs with 275μm gatewidth exhibited a current gain cutoff frequency (fT) of 32GHz and a maximum frequency of oscillation (fmax) of 150GHz; Under CW operating condition at 30GHz, the linear gain reaches 10.2dB. For the HEMTs with 675μm gatewidth, fT is 32GHz and fmax is 92GHz; Under CW operating condition at 30GHz, the linear gain reaches 8.5dB. The breakdown voltage is over 60V.