A high frequency transistor includes a first semiconductor layer, a first insulating film and a control electrode. The first semiconductor layer on the first insulating film extends in a first direction along an upper surface of the first insulating film. The first semiconductor layer has a first layer thickness in a second direction perpendicular to the upper surface, and a first width in a third direction orthogonal to the first direction. The first width is greater than the first layer thickness. The control electrode covers upper and side surfaces of the first semiconductor layer. The first semiconductor layer includes a first region of a first conductivity type, second and third regions of a second conductivity type. The first to third regions are arranged in the first direction. The first region is provided between the second and third region. The control electrode covers the first region.