A bipolar junction transistor (BJT) includes a semiconductor substrate and a first isolation structure. The semiconductor substrate includes a first fin structure disposed in an emitter region, a second fin structure disposed in a base region, and a third fin structure disposed in a collector region. The first, the second, and the third fin structures are elongated in a first direction respectively. The base region is adjacent to the emitter region, and the base region is located between the emitter region and the collector region. The first isolation structure is disposed between the first fin structure and the second fin structure, and a length of the first isolation structure in the first direction is shorter than or equal to 40 nanometers. An effective base width of the BJT may be reduced by the disposition of the first isolation structure, and a current gain of the BJT may be enhanced accordingly.

A bipolar junction transistor (BJT) device includes a semiconductor substrate, a first doping region with a first conductivity, a second doping region with a second conductivity, a third doping region with the first conductivity, at least one stacked block and a conductive contact. The first doping region is formed in the semiconductor substrate. The second doping region is formed in the first doping region. The at least one stacked block is formed on and insulated from the second doping region. The third doping region is formed in the second doping region and disposed adjacent to the at least one stacked block. The conductive contact electrically connects the at least one stacked block with the third doping region.

Methods for fabricating a bipolar junction transistor (BJT) are provided. A method includes forming a collector region, forming base regions over the collector region, and forming emitter regions over the base regions. The method further includes forming base dielectric layers over the collector region and on opposite sides of the base regions, forming base conductive layers over the base dielectric layers and on the opposite sides of the base regions, and forming base contacts over the base conductive layers. The top surface of the collector region is coplanar with bottom surfaces of the base regions and bottom surfaces of the base dielectric layers. The base contacts are divided into a first group of base contacts disposed between the base regions and a second group of base contacts disposed between the base regions and the STI region.

Bipolar transistors and MOS transistors are formed in a common process. A semiconductor layer is arranged on an insulating layer. On a side of the bipolar transistors: an insulating region including the insulating layer is formed; openings are etched through the insulating region to delimit insulating walls; the openings are filled with first epitaxial portions; and the first epitaxial portions and a first region extending under the first epitaxial portions and under the insulating walls are doped. On the side of the bipolar transistors and on a side of the MOS transistors: gate structures are formed; second epitaxial portions are made; and the second epitaxial portions covering the first epitaxial portions are doped.

A semiconductor device includes a first electrode, a first semiconductor region disposed on and electrically connected to the first electrode, a second semiconductor region disposed on the first semiconductor region and having a carrier concentration lower than that of the first semiconductor region, a third semiconductor region disposed on the second semiconductor region, a fourth semiconductor region disposed on the third semiconductor region, a fifth semiconductor region disposed on the second semiconductor region and separated from the third semiconductor region in a direction, a gate electrode disposed on the second semiconductor region, facing the third semiconductor region via an insulating layer in the direction and positioned between the third and fourth semiconductor regions, a second electrode disposed on and electrically connected to the fourth semiconductor region, and a third electrode disposed on the fifth semiconductor region, separated from the second electrode, and electrically connected to the fifth semiconductor region.

A bipolar junction transistor (BJT) includes a semiconductor substrate and a first isolation structure. The semiconductor substrate includes a first fin structure disposed in an emitter region, a second fin structure disposed in a base region, and a third fin structure disposed in a collector region. The first, the second, and the third fin structures are elongated in a first direction respectively. The base region is adjacent to the emitter region, and the base region is located between the emitter region and the collector region. The first isolation structure is disposed between the first fin structure and the second fin structure, and a length of the first isolation structure in the first direction is shorter than or equal to 40 nanometers. An effective base width of the BJT may be reduced by the disposition of the first isolation structure, and a current gain of the BJT may be enhanced accordingly.

A bipolar junction transistor (BJT) device includes a semiconductor substrate, a first doping region with a first conductivity, a second doping region with a second conductivity, a third doping region with the first conductivity, at least one stacked block and a conductive contact. The first doping region is formed in the semiconductor substrate. The second doping region is formed in the first doping region. The at least one stacked block is formed on and insulated from the second doping region. The third doping region is formed in the second doping region and disposed adjacent to the at least one stacked block. The conductive contact electrically connects the at least one stacked block with the third doping region.