Gate-all-around (GAA) transistors with an additional bottom channel for reduced parasitic capacitance and methods of fabricating the same include one or more channels positioned between a source region and a drain region. The one or more channels, which may be nanowire or nanoslab semiconductors, are surrounded by gate material. The GAA transistor further includes an additional semiconductor channel between a bottom section of a gate material and a silicon on insulator (SOI) substrate in a GAA transistor. This additional channel, sometimes referred to as a bottom channel, may be thinner than other channels in the GAA transistor and may have a thickness less than its length.