A multi-channel transistor device and a method of manufacturing the same are provided. The method of a manufacturing a multi-channel transistor device includes defining an active region in a semiconductor substrate by forming an isolation layer exposing an upper side portion of the active region. An active expanding region is formed on the exposed upper side portion of the active region by selective epitaxial growth (SEG). A portion of the active region is selectively etched to define first channel bars in the active expanding region that extend between first and second laterally separated portions of the active region and a second channel bar that is an unetched portion of the active region. A portion of the isolation layer is selectively removed such as to expose side portions of the second channel bar and bottom surface portions of the first channel bars. A gate is formed on the first and second channel bars with a gate dielectric layer between the gate and the channel bars. A source/drain region is formed in a region of the active expanding region adjacent to the gate, thereby resulting in a multi-channel transistor structure.