2SC3997 Bipolar Transistor

• Type: NPN
• Collector-Emitter Voltage, max: 800 V
• Collector-Base Voltage, max: 1500 V
• Emitter-Base Voltage, max: 6 V
• Collector Current − Continuous, max: 20 A
• Collector Dissipation: 250 W
• DC Current Gain (h_fe): 8 to 30
• Operating and Storage Junction Temperature Range: -55 to +150 °C
• Package: TO-3P

Here is an image showing the pin diagram of this transistor.Sometimes the "2S" prefix is not marked on the package - the 2SC3997 might only be marked "C3997".You can replace the 2SC3997 with the 2SC3998.