A method of forming a group III-V material layer, a semiconductor device including the group III-V material layer, and a method of manufacturing the semiconductor device. The semiconductor device includes a substrate; a group III-V channel layer formed on the substrate; a gate insulating layer formed on the group III-V channel layer; and a gate electrode and source and drain electrodes formed on the gate insulating layer, the source and drain electrodes having intervals from the gate electrode, wherein voids exist between a lower portion of the group III-V channel layer and an insulating layer. The group III-V channel layer may include a binary, ternary, or quaternary material.