Theoretical analysis of the detection of modulated sub-terahertz and terahertz radiation by a short channel field effect transistor (FET) predicts a very high upper limit for modulation frequency, Omega(max), up to 100 GHz or even higher. Even the minimal value of Omega(max), which is reached deep below the threshold, lies in the gigahertz range, thus promising for usage of FET-based structures for ultrafast detection of modulated terahertz radiation (c) 2007 Elsevier Ltd. All rights reserved.