Abstract The fabrication of InAs TFT's is described, the device characteristics are analyzed and related to the material properties. The transistor fabricated with a channel length of 10 −2 cm is a depletion type device which requires V 0 = −4.5 V gate voltage for pinch-off. From this value a carrier concentration of 8.0 × 10 16 /cm 3 in the InAs film is derived. With typical values for transconductance g m = 5.5 × 10 −3 A/V and for dynamic output resistance r ds = 20 k ω a voltage amplification factor of 110 was obtained although the following best individual values g m = 1.2 × 10 −2 A/V and r ds = 40 kω were achieved. From the transconductance and the saturated drain current, a field-effect mobility of 3000 cm 2 /V-sec was deduced. The gain-bandwidth product was measured and found to be 3 MHz. This result confirms the large value of the field-effect mobility for an InAs TFT having a channel length of 10 −2 cm if the gate capacitance of 200 pF is taken into account. Shortening the channel length to 5 × 10 −3 cm yielded a transconductance g m = 4.2 × 10 −2 A/V from which a field-effect mobility μ F = 7350 cm 2 /V-sec was computed, hence assuring a gain-bandwidth product of 250 MHz if the surface state density is slightly more reduced. An inverted TFT design, the feasibility of which is experimentally demonstrated, is necessary to obtain a gain-bandwidth product of 1 GHz since then the coarse crystalline InAs films having Hall mobilities μ H = 10,000 cm 2 /V-sec can be used. Such TFT's do not require a channel length smaller than 2 × 10 −3 cm, thus the drift mobility is not field dependent, hence UHF TFTs built with ease of fabrication can confidently be expected.