Voltage spike on 555 Output At 150Khz or am I reading this wrong?

Input voltage is 5V. How can this even happen unless it is acting like a charge pump? Is this a problem for 5V electronics?

More likely it’s problem with your oscilloscope. Have it been calibrated at least ones?

It's called "ringing"... or "ringing transients". Usually happens with square waves. (see gibbs phenomenon)

You can reduce/eliminate it by adding an appropriate resistor load to "dampen" it. But not too low a value... otherwise, it will go from a "spike" to a rounded square edges. -- which we also don't want, we want to stay close to a square wave as much as possible.

Is this a problem for 5V electronics?

It's a problem with square waves. It also happens in audio pre/amplifiers if it's not properly designed or terminated (either at it's input or output terminals, or both). (In amplifiers, you'll also have a ringing/spike on the downward going signal.)

The oscilloscope was self-calibrated when I received it and came with a calibration cert anyway. I haven't used it a great deal and I doubt it is out of spec. I will try running that through a resistor. I have no idea what an appropriate value is but I can try a few.

What do you have connected to the 555 output, apart from the oscilloscope?

That is ringing caused by inductance. The inductance is either in your load you are switching or caused by the oscilloscope lead. A high impedance scope probe often reduces the appearance of this. You have to adjust the probe's compensation screw to get it right.

Is this a problem for 5V electronics?

It is a problem of inductance on the output.

A smaller serial resistor (11 - 47ohm) will cure it.