Its a Thermal Fuse. This is DIY as the cost to get a serviceman out was 168.00 for me. The parts are 24.50 online or 45.00 in a parts store.
There are numerous forums where you can get instructions
If you do get a serviceman out, make sure s/he doesn't break the heating element, like mine did when he removed and replaced it . Now some of the element is warped and touches the side of its metal housing, shorting it to ground and blowing the main breaker.
If yours does this, then you need a new element.
FYI This dryer is made for Sears, and will fall under their warranty, service etc.
Frustrated, December 2009