In order to achieve low contact resistances of InAs/AlSb heterostructures with the undoped InAs cap layer, Pd/Ti/Pt/Au alloyed ohmic contact has been investigated. The contact resistance Rc is evaluated by using transmission-line-model (TLM) measurements. A minimum of 0.128 Ω·mm has been obtained by using the optimal rapid thermal annealing (RTA) with the condition at temperature of 275 °C and annealing time of 20 s. The measurement from transmission electron microscopy (TEM) demonstrates that the Pd atoms diffuses into the semiconductor, which is beneficial to the formation of a high-quality ohmic contact during the rapid thermal annealing. This study shows that the contact resistance Rc is reduced significantly after Pd/Ti/Pt/Au alloyed ohmic contact, which is suitable for its application in InAs/AlSb heterostructures.