I'm an unable to understand the difference between Step Fixed Cost and Semi Variable Cost?
I was of the opinion that step cost relates with the capacity where as semi variable with the production level, but now I feel there is anyb other difference, is it?
whether semi variable will always have a fixed portion?

There is a notable difference. See below:

Semi-variable costs are fixed below a certain level of volume, known as the breakpoint, and they are variable above that level. As explained, these costs act differently over a range of volume. Therefore, their volume variance behaves similarly: volume variance is zero in the fixed cost range, and volume variance is the same as for a variable cost over the variable cost range.

Step-fixed costs are fixed up to a certain level of volume, and then they increase to an even higher level of fixed cost to a certain level of volume. This process is repeated over and over with fixed costs increasing to higher levels. When dealing with step-fixed costs it is important to recognize at what points costs increase and to what levels they increase. Once this is accomplished, the volume variance is what the cost is suppose to be at budgeted volume minus what the cost is supposed to be at actual volume.

Can give the example of step fixed cost?
Bside rental fees...
Thanks a lot