Silicon industry has been doing very successfully in the last decades mainly by scaling down the silicon devices. InAs nanowires (NWs) are competitive candidates for high performance n-type devices owing mainly to their high electron mobility. However, the ability to improve the performance of InAs NW field effect transistors (FETs) through scaling down has not been studied a lot. To make things complicated, InAs NWs may have zinc blend (ZB) or wurtzite (WZ) phases, or even mixture of ZB and WZ phases when their diameters are different. Our previous studies demonstrate excellent off characteristics and enhancement-mode in FETs based on ultrathin (with sub-10 nm diameter) InAs NWs having pure WZ structure.[1, 2] High Ion/Ioff ratio up to 108, and subthreshold swing of 120 mV/decade have been observed. Diameter-dependent property changes have been studied and quantum confinement effects have been considered. Here, we study the effect of shortening the channel length of the InAs NWs FETs. FETs with the channel length down to tens of nanometers are fabricated and studied. Ballistic transport is observed in short channel devices. The effects of different phases are also studied. Reference:  Mengqi Fu, Dong Pan, Yingjun Yang, Tuanwei Shi, Zhiyong Zhang, Jianhua Zhao, H. Q. Xu and Qing Chen*, Appl. Phys. Lett. 105 (2014) 143101.  D. Pan, M. Q. Fu, X. Z. Yu, X. L. Wang, L. J. Zhu, S. H. Nie, S. L. Wang, Q. Chen, P. Xiong, S. von Molnï¿½r, J. H. Zhao, Nano Lett., 14(2014), 1214.