SOT-23

A small outline transistor (SOT) is a small footprint, discrete surface mount transistor commonly used in consumer electronics. Many manufacturers also offer the nearly identical thin small outline transistor (TSOT) package for use in electronic circuits where height is an important consideration.

The SOT23-3 package is very popular and a common package for transistors, and is also used for diodes and voltage regulators.

The SOT89-3 electrically only has three leads (contact/pin). The wide lead (tab) is physically part of the middle lead on the other side of the package. Some call this package a SOT89-4, since it visually appears to have four leads when looking down at the part.

The SOT89-5 electrically only has five leads (contact/pin). The middle lead is physically part of the middle lead on the other side of the package. Some call this package a SOT89-6, since it visually appears to have six leads when looking down at the part.

The SOT223-4 package is a popular package for voltage regulators.

The SOT223-5 package is a popular package for voltage regulators.

The SOT223-8 package is a popular package for bridged quad transistors.

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Wikipedia