Abstract: A safety interlock system for microwave ovens comprising first and second interconnected switches activated by the oven door. Each switch has make-and-break contacts. The first switch interrupts the current to the microwave source when the door is opened and the second switch monitors the operation of the first switch. The switches are connected in series with a fuse so that a malfunction of either of the switches makes the oven immediately unusable. A delay element is connected within one switch and the first switch is arranged to operate before the second switch when the door is initially opened. The delay element is a negative temperature coefficient (N.T.C) resistor.