I want to use a transistor to switch on and off a 6 volt dc motor (7 amps max) using a microcontroller. Thta's it - nice and simple... On and off. Will this transistor do the job? The current ratings are fine, but I am not familiar with all the other stats. Will a microcontroller be able to "turn on" (sorry, don't know the actual term) the transistor, and will it be ok with running 6 volts trhough it?

MJE2955T

http://www.farnell.com/datasheets/64761.pdf

 

The motor needs 7A but a PIC micro-controller can supply only 25mA.
A MJ2955 or 2N3055 needs a base current of about 1.75A to saturate with a 7A collector current. 70 times more than the PIC can provide. The transistor has a high voltage loss to the motor.
Use a logic-level Mosfet instead.