I have a 12V that I want to turn on and off using the IRF520 mosfet. Below I have a wiring diagram, but if I bring 12V + to the (G) gate, the mosfet will heat up in a few seconds and break through. I have an IRF520 from Aliexpress. Then I have one original and it works fine. Is there a possibility that the one from China will work? Using for example a 12V + resistor on the gate?
The bulb has 12V / 1A, so it should definitely not overheat the mosfet.
Not if it's destroyed.
What's the purpose of that mosfet in your circuit if you are switching 12V anyway using that switch? The mosfet is redundant in that circuit.
Can you post a photo of the circuit as you built it, with all the connections showing clearly?
Of course, I threw away the damaged mosfet. I have more IRF520 pieces from China.
The button on the diagram can handle a maximum of 0.2A / 12V, so to switch on a larger load, I use the IRF520 mosfet, which I have at home.
Then you have to connect +12V directly to the lamp and the switch only to the MOSFET gate.
So possibly it's also fried as you're currently using it to switch a 1A load.
Unless of course the schematic does not reflect the circuit as you built it.
The IRF520 datasheet lists VGS as ± 20 Volts for a real IRF520. So 12 V on the gate is no problem.
Either you did something rather foolish, or it was not actually an IRF520. You figure. 
But not with that circuit. 
Note that using a 100V MOSFET for a 12V circuit is a poor choice - performance goes down with increasing voltage for MOSFETs, which explains the very high on-resistance of the the IRF520 (its also an ancient device, pretty much as obsolete as they come for a MOSFET).
Usually you want logic-level MOSFETs just for the convenience factor, and unless you are driving high voltages a 30 to 50V drain-source rating is plenty.
These days semiconductors bought from dodgy sources are nearly universally counterfeit. You need to source from a reputable local supplier.
But would that not be the reason they are on all those websites as "disposals" items? 
Hmmm...not always, I think. It really depends. I've had ATMega328P's and PB's which are indistinguishable from the real thing - and as far as I can tell, they are either the real thing or perfect copies. I've had a number of TI chips and chips from other mfrs. with the same story - either real, or close enough to perfect to not be noticeable. The only case in which I've been able to establish that I had 'fakes' is with DS18B20's, which are nearly invariably fake if you get them from AliExpress. For the application I needed them it wasn't a problem, but in this case the fakes are indeed inferior to the real ones. And then of course there are the many IC's, including some I use frequently, that are originally Chinese and unlikely to be fake in the first place due to the absence of (costly to license) Western intellectual property.
Why anyone would bother to fake an IRF520 is entirely beyond me; as stated it's technology from the early 1990s, so cheap in any case and even if someone would want to fake it, it would be relatively easy for any 'suspect' manufacturer to make a device with superior performance to the original IRF520.
Where do you suppose the IP came from in the first place?
Like this?
Right.
What mosfet would you use instead of the old IRF520 on my used 12V?
That depends on the specific product. I didn't mention one.
One that's logic level, and has a low enough on-resistance. It could be as low as 20V rated for use at 12V (although I'd use a higher voltage rating if the load is inductive, which also needs a free-wheel diode across the load).
There are literally many 1000's of MOSFETs available, I do a parametric search when needed.
However many Arduino parts providers will have something that's at least 30V rated with on-resistance around 10 to 30 milliohms - that's going to usable for many situations of upto 10A.
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