Look at the 'days to emerge' on the package.... 10 - 15. You say you sowed them on October 26th - today is November 7th ie 12 days. So even under optimal conditions they would not necessarily be up yet.

However, they may not be in optimal conditions. Is November the right time to sow onions in Arizona? What 'soil' did you use? What is the temperature? And what exactly do you mean by 'packed'? You don't need to pack seed mix down hard.

Can you answer these questions and show a picture of your set up?

I am new to gardening. I'm still getting familiar with the words used. I just moved to Arizona, which is a semi-desert, hence I have to learn a lot for planting here.

According to one of the planting calendars, oct/nov is the time to plant onion seeds in the location I am living. But the temperatures have been higher than usual this year. Right now it is around 31C High and a 17C low. What is the best temperature for onions to germinate? I actually had my seed tray in a warm area. Is that wrong?

By Packed I meant:

When I sowed the seeds, I filled the cell in the stray, pushed it down with the thumb, then filled soil loosely over it. Put a hole and put 2 to 3 seeds.

This is the soil I used:

Well my conditions are about as far removed from Arizona as it is possible to get so I can't help much with timing. But your mix and technique seem fine. You did water after sowing didn't you?

Maybe if you go over to the Vegetable Gardening Forum you can get some more targeted advice suitable to your region. It is a much busier forum than this one.