S8550 is a PNP transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. It has a maximum gain value of 300; this value determines the amplification capacity of the transistor normally S8550. Since it is very high it is normally used for amplification purposes.
Low Voltage, High Current PNP Transistor
Continuous Collector current (IC) is 500mA
Collector-Emitter voltage (VCEO) is -25 V
Collector-Base voltage (VCB0) is -40V
Emitter Base Voltage (VBE0) is -5V
Current Gain (hFE), 85 to 300
Commonly used as Class B Push-pull transistors
Available in To-92 Package