data logging current

I need to datalog the current of a GaN gate during a transient test. The level is microamps at about -20 V. Your typical GPIB DMM (34401A, et al) will do it, but I need 10's of kHz of BW, not 3-4 a second. Is a series resistor and scope my only option?

How many samples at what sample rate would be needed? (And what resolution?)

I would like at least 3.5 - 4 digit resolution*. As for the rest, I want to check out my options, since there are actually multiple tests. For the one I am thinking of, I would like 1 MHz sample rate and at least several mS of samples.

*though I know I will probably have to settle for 8-12 bits.

What are you using for a current sensor to convert to voltage ?

Nothing at this point, that is the whole problem. 8^) The last time I was using an SMU and just used a clipboard and mark I eyeball to try to figure out the peak current during the transient.