The inverter includes a driving transistor and a loading transistor having channel regions with different thicknesses. The channel region of the driving transistor may be thinner than the channel region of the load transistor. A channel layer of the driving transistor may have a recessed region between a source and a drain which contact both ends of the channel layer. The driving transistor may be an enhancement mode transistor and the load transistor may be a depletion mode transistor.