We report on extremely scaled down tri-gate RF MOSFETs utilizing lateral nanowires as the channel, with gate length and nanowire width both of 20 nm. These devices exhibit simultaneous extrapolated ft and fmax of 275 and 400 GHz at VDS = 0.5 V, which is the largest combined ft and fmax, as well as the largest fmax reported for all III-V MOSFET. Introduction: Tri-gate (or non-planar) MOSFETs for RF-applications are motivated by that the use of a high-k oxide, rather than a semiconductor barrier

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... as in HEMTs) allows for higher gate capacitance in the MOSFET [1-2]. Furthermore, the tri-gate architecture improves short-channel effects, allowing for shorter gate length, LG, without degradation of performance due to short-channel effects. Both these points enable higher ideal transconductance, gm, in MOSFETs compared to HEMTs, assuming similar electron mobility. In fact, stateof-the-art III-V MOSFET devices exhibit gm larger than that of record HEMTs, although they presently do not allow RF-compatible device designs [3] [4] [5] . In this work, we present RF-compatible tri-gate In0.85Ga0.15As MOSFETs utilizing lateral nanowires (NWs) as the channel. Compared to our previous work, we have here further scaled down device dimensions, LG and nanowire width, WNW [6]. This enables higher gm at VDS = 0.5 V, which significantly improves ft/fmax from 220/305 GHz to 275/400 GHz. The combined ft and fmax, as well as the fmax of these devices represent the highest reported values for all III-V MOSFETs.