The DEM file extension is related to the Creator Simulator an original fault simulator. A *.dem file contains some kind of temporary data.
DEM file extension - Creator Simulator temporary file
What is dem file? How to open dem files?
File type specification:
The DEM file extension is also used by Creator Simulator, an original fault simulator, created by Tufts University's Department of Electrical and Computer Engineering.
It is a discrete-event concurrent fault simulator, meaning that it evaluates changes in the circuit only at specified time instances, but is able to evaluate several faults at once. Creator is a single-level simulator, meaning that it can only run simulations on gate level or behavioral models.
The .dem files are generated for temporary purposes.