In this paper, a 50-μm-pitch coplanar waveguide pattern for on-wafer high-frequency measurements on nanowire FET is used. The contact structure exhibits relatively large parasitic elements in comparison to the intrinsic device making a precise deembedding both necessary and challenging. A single InAs nanowire FET with a large gate length of 1.4 μm possesses after deembedding a maximum stable gain higher than 30 dB and a maximum oscillation frequency of 15 GHz. The gate length scaling of the nanowire transistor is modeled using the experimental transconductance data of a set of transistors and an analytical model. On this basis, both the device performance and the expectation of high-frequency measurements at small gate lengths are discussed.