Conventional InAs/AlSb HEMTs suffer from chemical instability in materials and high kink current. To avoid these drawbacks, this work proposes a novel layer structure of an InAsSb/AlSb HEMT and a novel two-step passivation process. Performance improvements are reduced dc output conductance by approximately 4.6 times at V(DS) = 0.5 V and I(D) = 100 mA/mm, and gate leakage to 1 x 10(-3) mA/mm from 4 at V(GS) = -1.2 V and V(DS) = 0.8 V compared with those of two InAs/AlSb HEMTs, one with the conventional one-step and the other with the proposed two-step passivation process. Both dc and rf performances show strong evidences of impact ionization suppression. (C) 2010 Elsevier Ltd. All rights reserved.