The invention relates to a semiconductor device having a vertical transistor bipolar structure of emitter, base, and collector formed in this order from a semiconductor substrate surface in a depth direction. The semiconductor device includes an electrode embedded from the semiconductor substrate surface into the inside and insulated by an oxide film. In the surface of the substrate, a first-conductivity-type first semiconductor region, a second-conductivity-type second semiconductor region, and a first-conductivity-type third semiconductor region are arranged, from the surface side, inside a semiconductor device region surrounded by the electrode and along the electrode with the oxide film interposed therebetween, the second semiconductor region located below the first semiconductor region, the third semiconductor region located below the second semiconductor region. The electrode is insulated from the first to third semiconductor regions, and current gain is variable through application of voltage to the electrode.