Last updated
GD241 PNP transistor in a TO-66 package. GD241 Transistor.jpg
GD241 PNP transistor in a TO-66 package.

TO-66 is a type of semiconductor package for devices with three pins, such as transistors. The shape is similar to the TO-3 package, but the size is smaller. [1] The TO-66 package is made entirely of metal and is commonly used by silicon controlled rectifiers and power transistors. [2]

A semiconductor package is a metal, plastic, glass, or ceramic casing containing one or more discrete semiconductor devices or integrated circuits. Individual components are fabricated on semiconductor wafers before being diced into die, tested, and packaged. The package provides a means for connecting the package to the external environment, such as printed circuit board, via leads such as lands, balls, or pins; and protection against threats such as mechanical impact, chemical contamination, and light exposure. Additionally, it helps dissipate heat produced by the device, with or without the aid of a heat spreader. There are thousands of package types in use. Some are defined by international, national, or industry standards, while others are particular to an individual manufacturer.


In electronics, TO-3 is a designation for a standardized metal semiconductor package used for power semiconductors, including transistors, silicon controlled rectifiers, and, integrated circuits. TO stands for "Transistor Outline" and relates to a series of technical drawings produced by JEDEC.

Silicon controlled rectifier semiconductor electronic device with three p-n junctions, mainly used in devices where the control of high power is demanded

A silicon controlled rectifier or semiconductor controlled rectifier is a four-layer solid-state current-controlling device. The principle of four-layer p–n–p–n switching was developed by Moll, Tanenbaum, Goldey and Holonyak of Bell Laboratories in 1956. The practical demonstration of silicon controlled switching and detailed theoretical behavior of a device in agreement with the experimental results was presented by Dr Ian M. Mackintosh of Bell Laboratories in January 1958. The name "silicon controlled rectifier" is General Electric's trade name for a type of thyristor. The SCR was developed by a team of power engineers led by Gordon Hall and commercialized by Frank W. "Bill" Gutzwiller in 1957.

Related Research Articles

Electronics physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter

Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter.

Integrated circuit electronic circuit manufactured by lithography; set of electronic circuits on one small flat piece (or "chip") of semiconductor material, normally silicon

An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. The integration of large numbers of tiny MOS transistors into a small chip results in circuits that are orders of magnitude smaller, faster, and less expensive than those constructed of discrete electronic components. The IC's mass production capability, reliability, and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs.

Semiconductor device fabrication manufacturing process used to create integrated circuits

Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically the metal-oxide-semiconductor (MOS) devices used in the integrated circuit (IC) chips that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications.

Transistor Basic electronics component

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

Moores law Heuristic law stating that the number of transistors on a integrated circuit doubles every two years

Moore's law is the observation that the number of transistors in a dense integrated circuit doubles about every two years. The observation is named after Gordon Moore, the co-founder of Fairchild Semiconductor and CEO of Intel, whose 1965 paper described a doubling every year in the number of components per integrated circuit, and projected this rate of growth would continue for at least another decade. In 1975, looking forward to the next decade, he revised the forecast to doubling every two years, a compound annual growth rate (CAGR) of 41.4%.

Semiconductor industry companies manufacturing semiconductor devices

The semiconductor industry is the aggregate collection of companies engaged in the design and fabrication of semiconductors. It formed around 1960, once the fabrication of semiconductor devices became a viable business. The industry's annual semiconductor sales revenue has since grown to over $481 billion, as of 2018. The semiconductor industry is in turn the driving force behind the wider electronics industry, with annual power electronics sales of £135 billion as of 2011, annual consumer electronics sales expected to reach $2.9 trillion by 2020, tech industry sales expected to reach $5 trillion in 2019, and e-commerce with over $29 trillion in 2017.

A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics. Such a device is also called a power device or, when used in an integrated circuit, a power IC.


The TO-92 is a widely used style of semiconductor package mainly used for transistors. The case is often made of epoxy or plastic, and offers compact size at a very low cost.


The TO-220 is a style of electronic package used for high-powered, through-hole components with 0.1 inches (2.54 mm) pin spacing. The "TO" designation stands for "transistor outline". TO-220 packages have three leads. Similar packages with two, four, five or seven leads are also manufactured. A notable characteristic is a metal tab with a hole, used in mounting the case to a heatsink, allowing the component to dissipate more heat than one constructed in a TO-92 case. Common TO-220-packaged components include discrete semiconductors such as transistors and silicon-controlled rectifiers, as well as integrated circuits.

2N3055 bipolar power transistor

The 2N3055 is a silicon NPN power transistor intended for general purpose applications. It was introduced in the early 1960s by RCA using a hometaxial power transistor process, transitioned to an epitaxial base in the mid-1970s. Its numbering follows the JEDEC standard. It is a transistor type of enduring popularity.

Transistor count the number of transistors in a device

The transistor count is the number of transistors on an integrated circuit (IC). It typically refers to the number of MOSFETs on an IC chip, as all modern ICs use MOSFETs. It is the most common measure of IC complexity. The rate at which MOS transistor counts have increased generally follows Moore's law, which observed that the transistor count doubles approximately every two years.

Texas Instruments Power, known more popularly by its acronym TIP, is a series of bipolar junction transistors manufactured by Texas Instruments. The series was introduced in the 1960s, and still sees some use today due to their simplicity, their durability, and their ease of use. A Texas Instruments catalog in 1966 lists the TIP04 and TIP14 part numbers.

A diffused junction transistor is a transistor formed by diffusing dopants into a semiconductor substrate. The diffusion process was developed later than the alloy junction and grown junction processes for making BJTs.

TO-18 style of transistor metal case

In electronics, TO-18 is a designation for a style of transistor metal case. The case is more expensive than the similarly sized plastic TO-92 package. The name is from JEDEC, signifying Transistor Outline Package, Case Style 18.


The D2PAK or DDPAK, standardized as TO-263, refers to a semiconductor package type intended for surface mounting on circuit boards. They are similar to the earlier TO-220-style packages intended for high power dissipation but lack the extended metal tab and mounting hole, while representing a larger version of the TO-252, also known as DPAK, SMT package. As with all SMT packages, the pins on a D2PAK are bent to lie against the PCB surface.

TO-5 designation for a standardized metal semiconductor package

In electronics, TO-5 is a designation for a standardized metal semiconductor package used for transistors and some integrated circuits. The TO element stands for "transistor outline" and refers to a series of technical drawings produced by JEDEC.


TO-126 is a type of semiconductor package for devices with three pins, such as transistors. The package is rectangular with a hole in the middle to allow for easy mounting to a board or a heat sink.


  1. TO-66 package details (PDF), Central Semiconductor Corp., 2008, retrieved 2013-12-09
  2. "TO-66 Package". Retrieved 8 February 2019.