A transistor includes a buffer layer, a channel layer over the buffer layer, a barrier layer over the channel layer, a source electrode electrically connected to the channel layer, a drain electrode electrically connected to the channel layer, a gate electrode on the barrier layer between the source electrode and the drain electrode, a backside metal layer, a substrate between a first portion of the buffer layer and the backside metal layer; and a dielectric between a second portion of the buffer layer and the backside metal layer.