The 2N3055 transistor is a silicon Epitaxial-Base Planar NPN transistor. These devices are used for switching the power
of the max value of IB and IC 7 A max 15 A. Usually it is applied for motor driver, power switching circuits, series and shunt regulators, output stages and high fidelity amplifiers.
as a 15 Ampere Complementary Silicon Power Transistors 60 V, 115 W,
featuring DC Current Gain − hFE = 20−70 @ IC = 4 Adc, VCE(sat) = 1.1 Vdc
(Max) @ IC = 4 Adc for its Collector−Emitter Saturation Voltage,
Excellent Safe Operating Area, and available in Pb−Free Packages. You
can see an Active Region Safe Operating Area (in a curve diagram) that must be observed for reliable operation due subjected to greater dissipation than the curves indicate.
Detailed information of ON Semiconductor 2N3055 Power Discrete Devices Datasheet can be downloaded in 4 pages/71 Kb of pdf filetype (source: onsemi.com)