Here's how I do it and it works for me! Nearly 100% effective too

.
For larger loads of lumber, I use my dry kiln to heat the wood to 140*F. for several hours at the end of the drying cycle. Photo 1
For small chunks and found wood, I use a small chamber made out of plywood 2' x 2' x 8'. I made this chamber so it could be taken apart when not in use.
I use a small electric space heater placed inside the chamber. I have a digital thermostat to regulate the temp. and a digital thermometer to check the temp. at the far end of the chamber. Photos 2 & 3
I heat the wood to 140*F. for about 8 hrs.
Someday I'll insert a temp probe into a sample block so when the temp. inside the block reaches 135*F. I'll know that I'll only have to cook the wood for 30 mins. to effectively kill any/ all insects, larve, eggs and or fungus.
The 4th photo is a picture of the bowl & ladle that I made from the gray looking block that was in the chamber in photo 2.
Just remember if you're using heat to sterilize your wood, you just want to heat it not dry the wood!