This is one of the transistor types.
Part Number : BD139
Description : Complementary Low Voltage Transistor
Package : SOT-32 Pin
Manufactures : STMicroelectronics
These epitaxial planar transistors are mounted in the SOT-32 plastic package. They are designed for audio amplifiers and drivers utilizing complementary or quasi-complementary circuits. The NPN types are the BD135 and BD139, and the complementary PNP types are the BD136 and BD140, BD139 Datasheet PDF.
Absolute maximum ratings ( Ta=25°C )
1. Products are pre-selected in DC current gain
2. General purpose