Small Outline Transistor (SOT) packages are very small, inexpensive surface-mount plastic-molded packages with leads on their two long sides. Due to their low cost and low profile, SOT's are widely used in consumer electronics.  The SOT-23 and the SC-70 packages are two of the most widely used SOT packages today. Note that aside from these two, there are many other SOT package types used in the IC industry.

Typical lead counts for the SOT-23 package range from 3 to 8, while typical lead counts for the SC-70 range from 3 to 6. Examples of typical dimensions of the SOT-23 and the SC-70 packages are shown in Table 1.

Note that in packages with odd lead counts, one side of the package has one less lead than the other side.  This results in lead spacing between two adjacent leads that is twice the normal lead pitch of the package. Some SOT packages have two different lead dimensions in the same package.  Such packages can have different lead pitch values, depending on which two adjacent leads they pertain to.