Most effective method of sterilization by heat is
Hot air
Boiling
Steam
Steam under pressure
Most effective method of sterilization by heat is by using moist heat (steam) above atmospheric pressure Autoclave is a classical example. Principle of autoclave- when water boils under pressure, instead of boiling at 100 degrees, it boils at a higher temperature. Hence the steam generated is at higher temperature.
General Microbiology (Sterilization and Bacterial Genetics)