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When did Bell Labs publicly announce the transistor?

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NMOS transistorNegative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors. — transistor NMOS transistor
Negative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors.

Bell Labs publicly announced the transistor in June 1948 during a press conference held at its New York City headquarters.1

While the invention was first demonstrated to observers at Bell Labs in December 1947, the formal public announcement occurred the following summer after the device had been named. Later, in July 1951, Bell Labs held a separate announcement regarding the successful development of the junction transistor.12