Unit cells of metal oxide semiconductor (MOS) transistors are provided having an integrated circuit substrate and a MOS transistor on the integrated circuit substrate. The MOS transistor includes a source region, a drain region and a gate. The gate is between the source region and the drain region. A channel region is provided between the source and drain regions. The channel region has a recessed region that is lower than bottom surfaces of the source and drain regions. Related methods of fabricating transistors are also provided.