In a semiconductor optical device, the first conductive type semiconductor region includes a first semiconductor portion and a second semiconductor portion. The first and second regions of the first semiconductor portion are arranged along a predetermined plane. The second semiconductor portion is provided on the first region of the first semiconductor portion. The active layer is provided on the second semiconductor portion of the first conductive type semiconductor region. The second conductive type semiconductor region is provided on the second region of the first semiconductor portion of the first conductive type semiconductor region. The side of the second semiconductor portion of the first conductive type semiconductor region, the top and side of the active layer, the second region of the first conductive type semiconductor region and the second conductive type semiconductor region constitute a pn junction. The first distributed Bragg reflector portion includes first distributed Bragg reflector layers and second distributed Bragg reflector layers which are arranged alternately. The second distributed Bragg reflector portion includes third distributed Bragg reflector layers and fourth distributed Bragg reflector layers which are arranged alternately. The first conductive type semiconductor region, the active layer and the second conductive type semiconductor region are provided between the first distributed Bragg reflector portion and the second distributed Bragg reflector layers.