Today I was working with a 2n3055 NPN power transistor, according to the datasheet the DC current gain of the transistor should be in the range of 20-70 for the collector current upto 4A so I took my multimeter and measured the hfe i.e;DC current gain of the transistor and it shows 52.Then I took a 12v power supply connected a 1k ohm resistor from the supply to the base of 2n3055,grounded the emitter and connected the collector terminal also to the supply but the problem is I got a base current of 11.41 mA close to about 12mA but instead of getting collector current of 624mA(12×52) I got a collector current of 1.21A which means the DC current gain of the Transister has become about 100...but how is it possible,the max hfe specified by the datasheet is 70 so how can it be 100...I don't understand is there any mistake by me?or my Transister is damaged....please someone help me pretty much confused.

 

The gain will vary with base current, collector voltage, and temperature. Also there will be a spread of characteristics between transistors even at the same conditions. See the graph below from the datasheet.

 

Note that the graph in post #2 is for a "typical" device. At 4A, it's showing a beta of around 35, but the datasheet gives a range of 20-70.

Most would complain if they didn't get the minimum beta, but a higher beta isn't usually a problem.