Provided is a structure of a sump assembly of a dishwasher. The dishwasher includes a tub forming a washing chamber, and a sump assembly provided at a lower side of the washing chamber and configured to store washing water in the washing chamber, wherein the sump assembly includes a sump housing having a water storage chamber storing the washing water and a sidewall portion forming the water storage chamber, and a heater provided on the sidewall portion to apply heat to the washing water stored in the sump assembly. The heater includes a planar heating element, and the planar heating element provided in a cylindrical shape forms the sidewall portion.