It seems you are referring to C945 (also written as 2SC945), a very common NPN bipolar junction transistor (BJT). The 2SC945 is mainly used for low-noise, low-frequency amplification and switching applications. It belongs to the same family of small-signal transistors as BC547/BC548 but is popular in Asian circuits and audio equipment. The C945 transistor has a collector-emitter voltage (Vce) of 50V, a collector current (Ic) of up to 150mA, and a DC current gain (hFE) typically between 70 and 700 depending on the variant (C945, C945A, etc.). It operates well in low-power audio amplifier stages, signal processing, preamplifiers, and small switching circuits. Its TO-92 package makes it suitable for breadboard use and PCB mounting. Because of its low noise figure, the C945 is often found in microphone amplifiers, radio circuits, and audio frequency devices, where clean signal amplification is needed. It can also be used as a switching transistor in digital and low-power control circuits.