Next-generation mobile systems will eventually be based on a vast range of innovative devices and components. Some of these devices, either electronic or optical, will play a key role in the system to support growing data traffic demand. In this paper, an analysis of silicon (Si) and gallium nitride (GaN) gate-all-around nanowire field-effect transistors employing different gate oxides is carried out. The analysis considers the impact of channel length decrease on the alternating current response of the devices. Simulated curves for the current-voltage and charge-voltage of the Si and GaN devices are used to obtain the following figures-of-merits: capacitance, transconductance, transconductance generation factor, and cut-off frequency for a channel length ranging from 30 to 200 nm. Numerical results shown that the GaN-based device has better performance than does Si-based device. The GaN-based device is a promising candidate for the development of ultra-fast response, low power consumption, and higher frequency operation to be used as part of the range of devices of next-generation mobile systems.