July 4, 1951

Transistor

Bell Labs announces the grown-junction transistor

Bell Labs waited more than a year to announce the device — and the working transistor had been grown as a single germanium crystal, its melt flipped from n-type to p-type and back with tiny pellets.

4 July 1951: the junction transistor goes public

On 4 July 1951, Bell Laboratories publicly announced its grown-junction transistor at a press conference featuring William Shockley. The device disclosed that day was a three-layer n-p-n germanium transistor — more rugged and practical than the point-contact transistor of 1947.

The announcement was of work already accomplished, not a same-day invention: sources place the working prototype in April 1950, with an etched specimen recorded in a 12 April notebook entry and a scholarly APS history dating the formal demonstration to 20 April.

Three names on the paper — and they aren't the famous three

The accompanying technical paper was authored by Shockley, Morgan Sparks and Gordon Teal — not by Shockley, Bardeen and Brattain. Shockley supplied the junction-transistor theory; Sparks and Teal fabricated the devices using Teal's single-crystal germanium growth technique.

Teal had built his crystal-growing equipment after failing to persuade many colleagues — including Shockley — that single crystals were essential. The published devices produced 50 decibels of power gain while operating at currents as low as 10 microamperes and voltages as low as 0.1 volt.

From press conference to production

The disclosure pointed Bell's development organization toward production, though a press announcement did not mean mature mass manufacturing existed that day. Part of the year-plus delay in announcing: early junction transistors were too slow at high frequencies.

Bardeen and Brattain's 1947 point-contact device remains the transistor's origin — and Bardeen, Brattain and Shockley shared the 1956 Nobel Prize in Physics — but the 1951 grown-junction announcement belongs to Shockley's theory and the fabrication work of Sparks and Teal.

Sources

Researched 23 Aug 2026 6 sources 3 audit passes

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

What the sources leave uncertain

Sources differ over which April 1950 date marks the prototype: an April 12 notebook entry records Sparks's etched specimen, while a scholarly APS history dates the formal demonstration to April 20. The July 4, 1951 public announcement is consistently reported.
The announcement should not be confused with the July 1 publication date of the Shockley–Sparks–Teal Physical Review paper.