The oven door inside glass has shattered and I was wondering if and how could I replace the inside glass pannel?

Only if it looks the same.

you have to get high temp glass or it will shatter

The glass is replaceable. You need to get the exact glass replacement kit from the manufacturer. I had to have mine replaced about a year ago due to condensation between the 2 glass panels and was able to get the replacement for $0.00.
Suggest to Siemens that the glass on yours should not have shattered and therefore was probably defective and you may luck out and get the glass for free. It's worth a try.

Very rare, in 35 years I replace maybe 2 to 5 a year out of 1500 to 2000 repairs a year on all major appliances. Make sure you replace it with the exact glass from the manufacturer, usuing your model number. Do not replace with glass from a glass shop.

Unfortunatey, it happens quite frequently, there is no one reason for it to do so.
The only solution is to replace it.
Over a number of years use, the glass looses it's properties, and this is what can happen.

We must have a model number to answer your question.

gget a new door

I have exactly the same problem and my bottom glass panel exploded. My friends did the same. You can take the inside glass panel out via the two screws and clean the inside of the outer glass once removed. Id replace all the rubber seals to as they perish, particularly the one that clips onto the oven itself that meets the door.

will need a model number to tell you the correct price ... most will have to replace the door... you can also give sears a call .. if you gripe loud ... they may replace it for you...