To-220 is a style of component package. TO refers to "transistor outline". TO-220 packages have three leads. Similar packages with two, four, five or seven leads are also manufactured. The power can reach 20W,25W,35W and 50W. TO-220 resistors are also called DIP power resistor or high voltage resistor. A metal tab with a hole is used to mount the case to a heatsink for dissipating waste heat.

Thermal compound is often applied to improve heat transfer from the package to the heatsink further. When the heatsink is electrically conductive, grounded or non-isolated, electrically insulating pad or sheet may be used to isolate the component from the heatsink. If more heat needs to be dissipated, devices in the also widely used TO-247 resistor can be selected.

 In applications that require a heatsink, damage or destruction of the TO-220 resistor may occur due to overheat if the heatsink is dislocated during operation. When a TO-220 package is used without a heatsink, the package acts as its own heatsink, and the heatsink-to-ambient thermal resistance in air for a TO-220 package is approximately 70 °C/W. If more heat needs to be dissipated, TO-247 resistors can be selected.

 To-220 resistors are widely used in EPU, electronic load, high frequency amplifier , electronic deceleration system and automotive fuel cell  due to the features of non-conductive, low thermal power, ultra small size, high power and easy to mount.