How the microwave oven has changed over time By etaggs Apr 10, 1920 Demonstrated at the Chicago World's Fair Apr 10, 1940 First prodotype Apr 10, 1940 early 6kW built Jan 1, 1946 First sold Apr 10, 1967 Counter top sold Apr 10, 1976 Built the first popular home model Apr 13, 2009 Made removable plates inside