A FinFET having fin back biasing and methods of forming the same are disclosed. The FinFET includes a substrate and a fin over the substrate. The fin includes a source region, a drain region, a channel region, and a biasing region. The source and drain regions sandwich the channel region. The channel region and the biasing region sandwich one of the source and drain regions. The FinFET further includes a gate over the substrate. The gate engages the fin adjacent to the channel region, thereby forming a field effect transistor (FET). The biasing region is configured to bias the FET body effect when a voltage is applied to the biasing region. From a cross sectional view, the source region and the biasing region each have a substantially rectangular profile, wherein the source region is taller and wider than the biasing region.