Type (NPN or PNP): Determine whether the original transistor is NPN or PNP.
Voltage Ratings: Look for a replacement with similar maximum collector-emitter voltage (Vce) and collector-base voltage (Vcb) ratings.
Current Ratings: Match the replacement transistor’s maximum collector current (Ic) with the original.
Power Dissipation: Ensure that the replacement has a comparable power dissipation capability.